| openwork | (noun) ornamental work (such as embroidery or latticework) having a pattern of openings | - |
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| opepe | (noun) large African forest tree yielding a strong hard yellow to golden brown lumber; sometimes placed in genus Sarcocephalus | Synonyms: Nauclea diderrichii, Sarcocephalus diderrichii |
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| opera | (noun) a building where musical dramas are performed | Synonyms: opera house |
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| (noun) a drama set to music; consists of singing with orchestral accompaniment and an orchestral overture and interludes | - |
| operable | (adjective) capable of being treated by surgical operation | - |
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| (adjective) usable for a specific purpose | Synonyms: practicable |
| (adjective) fit or ready for use or service | Synonyms: functional, operational, usable, useable |
| operagoer | (noun) a patron of the opera | - |
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| operand | (noun) a quantity upon which a mathematical operation is performed | - |
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| operant | (adjective) having influence or producing an effect | - |
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| operate | (verb) perform surgery on | Synonyms: operate on |
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| (verb) perform a movement in military or naval tactics in order to secure an advantage in attack or defense | Synonyms: maneuver, manoeuver, manoeuvre |
| (verb) handle and cause to function | Synonyms: control |
| (verb) keep engaged | Synonyms: engage, lock, mesh |
| (verb) perform as expected when applied | Synonyms: function, go, run, work |
| (verb) direct or control; projects, businesses, etc. | Synonyms: run |
| operatic | (adjective) of or relating to or characteristic of opera | - |
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| operating | (adjective) involved in a kind of operation | - |
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| (adjective) being in effect or operation | Synonyms: in operation, operational |
| operation | (noun) a medical procedure involving an incision with instruments; performed to repair damage or arrest disease in a living body | Synonyms: surgery, surgical operation, surgical procedure, surgical process |
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| (noun) (mathematics) calculation by mathematical methods | Synonyms: mathematical operation, mathematical process |
| (noun) activity by a military or naval force (as a maneuver or campaign) | Synonyms: military operation |
| (noun) a planned activity involving many people performing various actions | - |
| (noun) a process or series of acts especially of a practical or mechanical nature involved in a particular form of work | Synonyms: procedure |
| (noun) a business especially one run on a large scale | - |
| (noun) the activity of operating something (a machine or business etc.) | - |
| (noun) (psychology) the performance of some composite cognitive activity; an operation that affects mental contents | Synonyms: cognitive operation, cognitive process, mental process, process |
| (noun) (computer science) data processing in which the result is completely specified by a rule (especially the processing that results from a single instruction) | - |
| (noun) process or manner of functioning or operating | Synonyms: functioning, performance |
| (noun) the state of being in effect or being operative | - |
| operational | (adjective) (military) of or intended for or involved in military operations | - |
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| (adjective) pertaining to a process or series of actions for achieving a result | - |
| (adjective) being in effect or operation | Synonyms: in operation, operating |
| (adjective) fit or ready for use or service | Synonyms: functional, operable, usable, useable |
| operationalism | (noun) (philosophy) the doctrine that the meaning of a proposition consists of the operations involved in proving or applying it | - |
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| operationalist | (adjective) of or relating to or espousing operationalism | - |
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| operationally | (adverb) in respect to operation | - |
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| operations | (noun) financial transactions at a brokerage; having to do with the execution of trades and keeping customer records | Synonyms: trading operations |
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| operative | (adjective) being in force or having or exerting force | - |
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| (adjective) relating to or requiring or amenable to treatment by surgery especially as opposed to medicine | Synonyms: surgical |
| (adjective) (of e.g. a machine) performing or capable of performing | Synonyms: functional, running, working |
| (adjective) effective; producing a desired effect | - |
| (noun) someone who can be employed as a detective to collect information and assist in criminal investigations | Synonyms: PI, private detective, private eye, private investigator, shamus, sherlock |
| (noun) a person secretly employed in espionage for a government | Synonyms: intelligence agent, intelligence officer, secret agent |
| operatively | (adverb) in a manner to produce an effect | - |
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| operator | (noun) an agent that operates some apparatus or machine | Synonyms: manipulator |
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| (noun) someone who owns or operates a business | - |
| (noun) a shrewd or unscrupulous person who knows how to circumvent difficulties | Synonyms: hustler, wheeler dealer |
| (noun) a speculator who trades aggressively on stock or commodity markets | - |
| (noun) (mathematics) a symbol or function representing a mathematical operation | - |
| operculate | (adjective) having an operculum | Synonyms: operculated |
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| operculated | (adjective) having an operculum | Synonyms: operculate |
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| operculum | (noun) a hard flap serving as a cover for (a) the gill slits in fishes or (b) the opening of the shell in certain gastropods when the body is retracted | - |
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| operetta | (noun) a short amusing opera | Synonyms: light opera |
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| operon | (noun) a segment of DNA containing adjacent genes including structural genes and an operator gene and a regulatory gene | - |
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| operose | (adjective) characterized by effort to the point of exhaustion; especially physical effort | Synonyms: arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, punishing, toilsome |
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| operoseness | (noun) the quality of requiring extended effort | Synonyms: laboriousness, toilsomeness |
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| ophidian | (noun) limbless scaly elongate reptile; some are venomous | Synonyms: serpent, snake |
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| ophidism | (noun) poisoning by snake venom | - |
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| ophiolatry | (noun) the worship of snakes | Synonyms: serpent-worship |
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| ophryon | (noun) the craniometric point in the midline of the forehead immediately above the orbits | - |
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| ophthalmectomy | (noun) surgical removal of an eye | - |
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| ophthalmia | (noun) severe conjunctivitis | Synonyms: ophthalmitis |
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| ophthalmic | (adjective) of or relating to ophthalmology | - |
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| (adjective) of or relating to or resembling the eye | Synonyms: ocular, optic, optical |
| ophthalmitis | (noun) severe conjunctivitis | Synonyms: ophthalmia |
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| ophthalmologist | (noun) a medical doctor specializing in the diagnosis and treatment of diseases of the eye | Synonyms: eye doctor, oculist |
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| ophthalmology | (noun) the branch of medicine concerned with the eye and its diseases | - |
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| ophthalmoplegia | (noun) paralysis of the motor nerves of the eye | - |
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| ophthalmoscope | (noun) medical instrument for examining the retina of the eye | - |
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| ophthalmoscopy | (noun) examination of the interior of an eye using an ophthalmoscope | - |
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| opiate | (noun) a narcotic drug that contains opium or an opium derivative | - |
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| opine | (verb) expect, believe, or suppose | Synonyms: guess, imagine, reckon, suppose, think |
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| (verb) express one's opinion openly and without fear or hesitation | Synonyms: animadvert, sound off, speak out, speak up |
| opinion | (noun) the reason for a court's judgment (as opposed to the decision itself) | Synonyms: ruling |
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| (noun) a personal belief or judgment that is not founded on proof or certainty | Synonyms: persuasion, sentiment, thought, view |
| (noun) a belief or sentiment shared by most people; the voice of the people | Synonyms: popular opinion, public opinion, vox populi |
| (noun) a vague idea in which some confidence is placed | Synonyms: belief, feeling, impression, notion |
| (noun) the legal document stating the reasons for a judicial decision | Synonyms: judgement, judgment, legal opinion |
| (noun) a message expressing a belief about something; the expression of a belief that is held with confidence but not substantiated by positive knowledge or proof | Synonyms: view |
| opinionated | (adjective) obstinate in your opinions | Synonyms: opinionative, self-opinionated |
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| opinionative | (adjective) obstinate in your opinions | Synonyms: opinionated, self-opinionated |
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| opisthognathous | (adjective) having receding jaws | - |
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| opisthorchiasis | (noun) infestation with flukes obtained from eating raw fish; common in eastern Asia | - |
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| opisthotonos | (noun) severe spasm in which the back arches and the head bends back and heels flex toward the back | - |
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| opium | (noun) an addictive narcotic extracted from seed capsules of the opium poppy | - |
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| opopanax | (noun) an odorous gum resin formerly used in medicines | - |
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| opossum | (noun) nocturnal arboreal marsupial having a naked prehensile tail found from southern North America to northern South America | Synonyms: possum |
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| (noun) small furry Australian arboreal marsupials having long usually prehensile tails | Synonyms: phalanger, possum |
| oppa | (noun) a male who is older than the speaker, especially used by Korean female | - |
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| opponent | (adjective) characterized by active hostility | Synonyms: opposing |
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| (noun) someone who offers opposition | Synonyms: adversary, antagonist, opposer, resister |
| (noun) a contestant that you are matched against | Synonyms: opposite, opposition |
| opportune | (adjective) suitable or at a time that is suitable or advantageous especially for a particular purpose | - |
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| opportunely | (adverb) conveniently | - |
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| opportuneness | (noun) timely convenience | Synonyms: patness, timeliness |
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| opportunism | (noun) taking advantage of opportunities without regard for the consequences for others | Synonyms: expedience, self-interest, self-seeking |
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| opportunist | (adjective) taking immediate advantage, often unethically, of any circumstance of possible benefit | Synonyms: opportunistic, timeserving |
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| (noun) a person who places expediency above principle | Synonyms: self-seeker |
| opportunistic | (adjective) taking immediate advantage, often unethically, of any circumstance of possible benefit | Synonyms: opportunist, timeserving |
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| opportunity | (noun) a possibility due to a favorable combination of circumstances | Synonyms: chance |
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| opposable | (adjective) capable of being placed opposite to something | Synonyms: apposable |
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| oppose | (verb) be resistant to | Synonyms: contradict, controvert |
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| (verb) be against; express opposition to | - |
| (verb) set into opposition or rivalry | Synonyms: match, pit, play off |
| (verb) fight against or resist strongly | Synonyms: defend, fight, fight back, fight down |
| (verb) act against or in opposition to | Synonyms: react |
| (verb) contrast with equal weight or force | Synonyms: counterbalance |
| opposed | (adjective) being in opposition or having an opponent | - |
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| opposer | (noun) someone who offers opposition | Synonyms: adversary, antagonist, opponent, resister |
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| opposing | (adjective) characterized by active hostility | Synonyms: opponent |
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| opposite | (adjective) of leaves etc; growing in pairs on either side of a stem | Synonyms: paired |
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| (adjective) characterized by opposite extremes; completely opposed | Synonyms: diametric, diametrical, polar |
| (adjective) the other one of a complementary pair | - |
| (adjective) being directly across from each other; facing | - |
| (adjective) altogether different in nature or quality or significance | - |
| (adjective) moving or facing away from each other | - |
| (noun) a word that expresses a meaning opposed to the meaning of another word, in which case the two words are antonyms of each other | Synonyms: antonym, opposite word |
| (noun) a contestant that you are matched against | Synonyms: opponent, opposition |
| (noun) a relation of direct opposition | Synonyms: contrary, reverse |
| (noun) something inverted in sequence or character or effect | Synonyms: inverse |
| (adverb) directly facing each other | Synonyms: face-to-face, face to face |
| oppositely | (adverb) in an opposite position | - |
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| oppositeness | (noun) the relation between opposed entities | Synonyms: opposition |
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| opposition | (noun) the act of hostile groups opposing each other | Synonyms: confrontation |
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| (noun) the action of opposing something that you disapprove or disagree with | Synonyms: resistance |
| (noun) a body of people united in opposing something | - |
| (noun) an armed adversary (especially a member of an opposing military force) | Synonyms: enemy, foe, foeman |
| (noun) a contestant that you are matched against | Synonyms: opponent, opposite |
| (noun) a direction opposite to another | - |
| (noun) the relation between opposed entities | Synonyms: oppositeness |
| oppositionality | (noun) The quality of opposing or of being in conflict. | - |
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| oppositive | (adjective) expressing antithesis or opposition | Synonyms: adversative |
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| oppress | (verb) come down on or keep down by unjust use of one's authority | Synonyms: crush, suppress |
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| (verb) cause to suffer | Synonyms: persecute |
| oppressed | (adjective) burdened psychologically or mentally | Synonyms: laden |
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| oppression | (noun) the act of subjugating by cruelty | Synonyms: subjugation |
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| (noun) a feeling of being oppressed | Synonyms: oppressiveness |
| (noun) the state of being kept down by unjust use of force or authority: | - |
| oppressive | (adjective) marked by unjust severity or arbitrary behavior | Synonyms: tyrannical, tyrannous |
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| (adjective) weighing heavily on the senses or spirit | - |
| oppressively | (adverb) in a heavy and oppressive way | - |
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| oppressiveness | (noun) unwelcome burdensome difficulty | Synonyms: burdensomeness, heaviness, onerousness |
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| (noun) a feeling of being oppressed | Synonyms: oppression |
| oppressor | (noun) a person of authority who subjects others to undue pressures | - |
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| opprobrious | (adjective) (used of conduct or character) deserving or bringing disgrace or shame | Synonyms: black, disgraceful, ignominious, inglorious, shameful |
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| (adjective) expressing offensive reproach | Synonyms: abusive, scurrilous |
| opprobrium | (noun) a state of extreme dishonor | Synonyms: infamy |
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| (noun) state of disgrace resulting from public abuse | Synonyms: obloquy |
| oppugn | (verb) challenge the accuracy, probity, or propriety of | Synonyms: call into question, question |
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| opsin | (noun) retinal protein formed by the action of light on rhodopsin | - |
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| opsonin | (noun) an antibody in blood serum that attaches to invading microorganisms and other antigens to make them more susceptible to the action of phagocytes | - |
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| opsonisation | (noun) process whereby opsonins make an invading microorganism more susceptible to phagocytosis | Synonyms: opsonization |
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| opsonization | (noun) process whereby opsonins make an invading microorganism more susceptible to phagocytosis | Synonyms: opsonisation |
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| opsonize | (verb) make (cells) more susceptible to the action of phagocytes | - |
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| opt | (verb) select as an alternative over another | Synonyms: choose, prefer |
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| optative | (adjective) relating to a mood of verbs in some languages | - |
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| (adjective) indicating an option or wish | - |
| (noun) a mood (as in Greek or Sanskrit) that expresses a wish or hope; expressed in English by modal verbs | Synonyms: optative mood |
| optic | (adjective) of or relating to or resembling the eye | Synonyms: ocular, ophthalmic, optical |
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| (adjective) relating to or using sight | Synonyms: ocular, optical, visual |
| (noun) the organ of sight | Synonyms: eye, oculus |
| optical | (adjective) of or relating to or resembling the eye | Synonyms: ocular, ophthalmic, optic |
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| (adjective) of or relating to or involving light or optics | - |
| (adjective) relating to or using sight | Synonyms: ocular, optic, visual |
| optically | (adverb) in an optical manner | - |
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| optician | (noun) a worker who makes glasses for remedying defects of vision | Synonyms: lens maker |
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| optics | (noun) optical properties | - |
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| (noun) the branch of physics that studies the physical properties of light | - |
| optimal | (adjective) most desirable possible under a restriction expressed or implied | Synonyms: optimum |
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| optimally | (adverb) in an optimal and most desirable way | - |
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| optimisation | (noun) the act of rendering optimal | Synonyms: optimization |
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| optimise | (verb) act as an optimist and take a sunny view of the world | Synonyms: optimize |
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| (verb) make optimal; get the most out of; use best | Synonyms: optimize |
| (verb) modify to achieve maximum efficiency in storage capacity or time or cost | Synonyms: optimize |
| optimism | (noun) a general disposition to expect the best in all things | - |
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| (noun) the optimistic feeling that all is going to turn out well | - |
| optimist | (noun) a person disposed to take a favorable view of things | - |
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| optimistic | (adjective) expecting the best in this best of all possible worlds | - |
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| (adjective) expecting the best | Synonyms: affirmative |
| optimistically | (adverb) with optimism; in an optimistic manner | - |
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