| rein | (noun) one of a pair of long straps (usually connected to the bit or the headpiece) used to control a horse | - |
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| (noun) any means of control | - |
| relaxin | (noun) hormone secreted by the corpus luteum during the last days of pregnancy; relaxes the pelvic ligaments and prepares the uterus for labor | - |
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| renin | (noun) a proteolytic enzyme secreted by the kidneys; catalyzes the formation of angiotensin and thus affects blood pressure | - |
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| rennin | (noun) an enzyme that occurs in gastric juice; causes milk to coagulate | Synonyms: chymosin |
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| resin | (noun) any of a class of solid or semisolid viscous substances obtained either as exudations from certain plants or prepared by polymerization of simple molecules | Synonyms: rosin |
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| resorcinolphthalein | (noun) a yellow dye that is visible even when highly diluted; used as an absorption indicator when silver nitrate solution is added to sodium chloride in order to precipitate silver chloride (turns pink when no chloride ions are left in solution and negative fluorescein ions are then absorbed) | Synonyms: fluorescein, fluoresceine, fluorescent dye |
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| rhodopsin | (noun) a red photopigment in the retinal rods of vertebrates; dissociates into retinene by light | Synonyms: retinal purple, visual purple |
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| ribavirin | (noun) an inhaled antiviral agent (trade name Virazole) that may be used to treat serious virus infections | Synonyms: Virazole |
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| riboflavin | (noun) a B vitamin that prevents skin lesions and weight loss | Synonyms: hepatoflavin, lactoflavin, ovoflavin, vitamin B2, vitamin G |
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| ricin | (noun) a toxic protein extracted from castor beans; used as a chemical reagent; can be used as a bioweapon | Synonyms: ricin toxin |
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| rifampin | (noun) an antibacterial drug (trade names Rifadin and Rimactane) used to treat tuberculosis | Synonyms: Rifadin, Rimactane |
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| robin | (noun) large American thrush having a rust-red breast and abdomen | Synonyms: American robin, Turdus migratorius |
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| (noun) small Old World songbird with a reddish breast | Synonyms: Erithacus rubecola, Old World robin, redbreast, robin redbreast |
| rosin | (noun) any of a class of solid or semisolid viscous substances obtained either as exudations from certain plants or prepared by polymerization of simple molecules | Synonyms: resin |
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| ruin | (noun) destruction achieved by causing something to be wrecked or ruined | Synonyms: laying waste, ruination, ruining, wrecking |
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| (noun) a ruined building | - |
| (noun) an event that results in destruction | Synonyms: ruination |
| (noun) failure that results in a loss of position or reputation | Synonyms: downfall, ruination |
| (noun) the process of becoming dilapidated | Synonyms: dilapidation |
| (noun) an irrecoverable state of devastation and destruction | Synonyms: ruination |
| sabin | (noun) a unit of acoustic absorption equivalent to the absorption by a square foot of a surface that absorbs all incident sound | - |
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| saccharin | (noun) a crystalline substance 500 times sweeter than sugar; used as a calorie-free sweetener | - |
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| safranin | (noun) any of a class of chiefly red organic dyes | Synonyms: saffranine, safranine |
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| sainfoin | (noun) Eurasian perennial herb having pale pink flowers and curved pods; naturalized in Britain and North America grasslands on calcareous soils; important forage crop and source of honey in Britain | Synonyms: esparcet, holy clover, Onobrychis viciaefolia, Onobrychis viciifolia, sanfoin |
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| salicin | (noun) an anti-inflammatory agent that is produced from willow bark. | - |
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| saligenin | (noun) Salicylic alcohol, also called saligenin, is a crystalline phenolic alcohol with the chemical formula C7H8O2, that is obtained usually by hydrolysis of salicin. | Synonyms: salicylic alcohol |
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| salvinorin | (noun) a hallucinogen obtained from Salvia divinorum | - |
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| sanfoin | (noun) Eurasian perennial herb having pale pink flowers and curved pods; naturalized in Britain and North America grasslands on calcareous soils; important forage crop and source of honey in Britain | Synonyms: esparcet, holy clover, Onobrychis viciaefolia, Onobrychis viciifolia, sainfoin |
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| sannyasin | (noun) a Hindu religious mendicant | Synonyms: sannyasi, sanyasi |
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| saponin | (noun) any of various plant glucosides that form soapy lathers when mixed and agitated with water; used in detergents and foaming agents and emulsifiers | - |
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| sarin | (noun) a highly toxic chemical nerve agent that inhibits the activity of cholinesterase | Synonyms: GB |
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| satin | (noun) a smooth fabric of silk or rayon; has a glossy face and a dull back | - |
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| savarin | (noun) a sponge cake baked in a ring mold | - |
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| savin | (noun) procumbent or spreading juniper | Synonyms: dwarf juniper, Juniperus sabina |
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| saxitoxin | (noun) a powerful neurotoxin produced by certain dinoflagellates found in red tides; it can accumulate in mollusks that feed on the dinoflagellates and cause food poisoning to humans | - |
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| scarfpin | (noun) a pin used to hold the tie in place | Synonyms: tie tack, tiepin |
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| scatterbrain | (noun) a flighty and disorganized person | Synonyms: forgetful person |
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| scleroprotein | (noun) a simple protein found in horny and cartilaginous tissues and in the lens of the eye | Synonyms: albuminoid |
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| sculpin | (noun) any of numerous spiny large-headed usually scaleless scorpaenoid fishes with broad mouths | - |
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| sealskin | (noun) a garment (as a jacket or coat or robe) made of sealskin | - |
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| (noun) the pelt or fur (especially the underfur) of a seal | Synonyms: seal |
| searobin | (noun) American gurnard; mostly found in bays and estuaries | Synonyms: sea robin |
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| secretin | (noun) a gastrointestinal hormone that stimulates the secretion of water and bicarbonate from the pancreas and bile ducts whenever the stomach empties too much acid into the small intestine | - |
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| sequin | (noun) adornment consisting of a small piece of shiny material used to decorate clothing | Synonyms: diamante, spangle |
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| serin | (noun) any of various brown and yellow finches of parts of Europe | - |
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| serotonin | (noun) a neurotransmitter involved in e.g. sleep and depression and memory | Synonyms: 5-hydroxytryptamine |
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| sharkskin | (noun) a smooth crisp fabric | - |
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| sheepskin | (noun) a document certifying the successful completion of a course of study | Synonyms: diploma |
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| (noun) tanned skin of a sheep with the fleece left on; used for clothing | Synonyms: fleece |
| (noun) skin of a sheep or goat prepared for writing on | Synonyms: lambskin, parchment |
| shin | (noun) the inner and thicker of the two bones of the human leg between the knee and ankle | Synonyms: shin bone, shinbone, tibia |
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| (noun) the front part of the human leg between the knee and the ankle | - |
| (noun) the 22nd letter of the Hebrew alphabet | - |
| (noun) a cut of meat from the lower part of the leg | Synonyms: shin bone |
| siderophilin | (noun) a globulin in blood plasma that carries iron | Synonyms: beta globulin, transferrin |
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| simvastatin | (noun) an oral lipid-lowering medicine (trade name Zocor) administered to reduce blood cholesterol levels; recommended after heart attacks | Synonyms: Zocor |
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| sin | (noun) an act that is regarded by theologians as a transgression of God's will | Synonyms: sinning |
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| (noun) estrangement from god | Synonyms: sinfulness, wickedness |
| (noun) the 21st letter of the Hebrew alphabet | - |
| (noun) ratio of the length of the side opposite the given angle to the length of the hypotenuse of a right-angled triangle | Synonyms: sine |
| sirloin | (noun) the portion of the loin (especially of beef) just in front of the rump | - |
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| siskin | (noun) small yellow-and-black Eurasian finch with a sharp beak | Synonyms: Carduelis spinus |
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| skein | (noun) coils of worsted yarn | - |
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| skin | (noun) body covering of a living animal | Synonyms: hide, pelt |
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| (noun) an outer surface (usually thin) | - |
| (noun) a bag serving as a container for liquids; it is made from the hide of an animal | - |
| (noun) a natural protective body covering and site of the sense of touch | Synonyms: cutis, tegument |
| (noun) the rind of a fruit or vegetable | Synonyms: peel |
| (noun) a member of any of several British or American groups consisting predominantly of young people who shave their heads; some engage in white supremacist and anti-immigrant activities and this leads to the perception that all skinheads are racist and violent | Synonyms: skinhead |
| (noun) a person whose head is bald or shaved | Synonyms: baldhead, baldpate, baldy, skinhead |
| (noun) a person's skin regarded as their life | - |
| slain | (noun) people who have been slain (as in battle) | - |
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| smidgin | (noun) a tiny or scarcely detectable amount | Synonyms: iota, scintilla, shred, smidge, smidgen, smidgeon, tittle, whit |
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| somatotrophin | (noun) a hormone produced by the anterior pituitary gland; promotes growth in humans | Synonyms: growth hormone, human growth hormone, somatotrophic hormone, somatotropic hormone, somatotropin, STH |
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| somatotropin | (noun) a hormone produced by the anterior pituitary gland; promotes growth in humans | Synonyms: growth hormone, human growth hormone, somatotrophic hormone, somatotrophin, somatotropic hormone, STH |
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| soupfin | (noun) Pacific shark valued for its fins (used by Chinese in soup) and liver (rich in vitamin A) | Synonyms: Galeorhinus zyopterus, soup-fin, soupfin shark |
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| spavin | (noun) a swelling of the hock joint of a horse; resulting in lameness | - |
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| spectinomycin | (noun) an antibiotic used to treat gonorrhea | - |
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| spillikin | (noun) a thin strip of wood used in playing the game of jackstraws | Synonyms: jackstraw |
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| spin | (noun) the act of rotating rapidly | Synonyms: twirl, twist, twisting, whirl |
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| (noun) a short drive in a car | - |
| (noun) rapid descent of an aircraft in a steep spiral | Synonyms: tailspin |
| (noun) a distinctive interpretation (especially as used by politicians to sway public opinion) | - |
| (noun) a swift whirling motion (usually of a missile) | - |
| sprain | (noun) a painful injury to a joint caused by a sudden wrenching of its ligaments | - |
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| stain | (noun) an act that brings discredit to the person who does it | Synonyms: blot, smear, smirch, spot |
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| (noun) a soiled or discolored appearance | Synonyms: discoloration, discolouration |
| (noun) a symbol of disgrace or infamy | Synonyms: brand, mark, stigma |
| (noun) anything regarded as making something unclean | Synonyms: dirt, filth, grease, grime, grunge, soil |
| (noun) (microscopy) a dye or other coloring material that is used in microscopy to make structures visible | - |
| statin | (noun) a medicine that lowers blood cholesterol levels by inhibiting HMG-CoA reductase | Synonyms: lipid-lowering medication, lipid-lowering medicine, statin drug |
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| stearin | (noun) an ester of glycerol and stearic acid | - |
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| stein | (noun) a mug intended for serving beer | Synonyms: beer mug |
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| stickpin | (noun) a decorative pin that is worn in a necktie | - |
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| strain | (noun) an effortful attempt to attain a goal | Synonyms: nisus, pains, striving |
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| (noun) the act of singing | Synonyms: song |
| (noun) an intense or violent exertion | Synonyms: straining |
| (noun) the general meaning or substance of an utterance | Synonyms: tenor |
| (noun) a succession of notes forming a distinctive sequence | Synonyms: air, line, melodic line, melodic phrase, melody, tune |
| (noun) a special variety of domesticated animals within a species | Synonyms: breed, stock |
| (noun) (biology) a group of organisms within a species that differ in trivial ways from similar groups | Synonyms: form, var., variant |
| (noun) (physics) deformation of a physical body under the action of applied forces | - |
| (noun) injury to a muscle (often caused by overuse); results in swelling and pain | - |
| (noun) (psychology) nervousness resulting from mental stress | Synonyms: mental strain, nervous strain |
| (noun) difficulty that causes worry or emotional tension | Synonyms: stress |
| streptolysin | (noun) any of several hemolysins derived from strains of streptococcus | - |
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| streptomycin | (noun) an antibiotic produced by the actinomycete Streptomyces griseus and used to treat tuberculosis | - |
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| streptothricin | (noun) a basic antibiotic derived from a soil actinomycete | - |
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| strophanthin | (noun) a bitter and very toxic glycoside derived from plants of the genus Strophanthus; in moderate doses it is a cardiac stimulant but in larger doses it is a powerful poison; used in Africa as an arrow poison | - |
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| subtilin | (noun) a polypeptide antibiotic (similar to bacitracin) obtained from a soil bacterium | - |
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| supervillain | (noun) a villain with superpowers | - |
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| suzerain | (noun) a state exercising a degree of dominion over a dependent state especially in its foreign affairs | - |
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| swain | (noun) a man who is the lover of a man or woman | Synonyms: beau, boyfriend, fellow |
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| tailfin | (noun) a stabilizer that is part of the vertical tail structure of an airplane | Synonyms: tail fin, vertical fin, vertical stabiliser, vertical stabilizer |
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| (noun) one of a pair of decorations projecting above the rear fenders of an automobile | Synonyms: fin, tail fin |
| tailspin | (noun) rapid descent of an aircraft in a steep spiral | Synonyms: spin |
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| (noun) loss of emotional control often resulting in emotional collapse | - |
| takin | (noun) large heavily built goat antelope of eastern Himalayan area | Synonyms: Budorcas taxicolor, gnu goat |
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| talapoin | (noun) smallest guenon monkey; of swampy central and west African forests | Synonyms: Cercopithecus talapoin |
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| tamarin | (noun) small South American marmoset with silky fur and long nonprehensile tail | Synonyms: leoncita, lion marmoset, lion monkey |
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| tannin | (noun) any of various complex phenolic substances of plant origin; used in tanning and in medicine | Synonyms: tannic acid |
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| tarpaulin | (noun) waterproofed canvas | Synonyms: tarp |
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| tefillin | (noun) (Judaism) either of two small leather cases containing texts from the Hebrew Scriptures (known collectively as tefillin); traditionally worn (on the forehead and the left arm) by Jewish men during morning prayer | Synonyms: phylactery |
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| tenderloin | (noun) the tender meat of the loin muscle on each side of the vertebral column | Synonyms: undercut |
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| (noun) a city district known for its vice and high crime rate | Synonyms: combat zone |
| tenpin | (noun) one of the bottle-shaped pins used in bowling | - |
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| terazosin | (noun) antihypertensive drug (trade name Hytrin) used to treat high blood pressure | Synonyms: Hytrin |
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| terrain | (noun) a piece of ground having specific characteristics or military potential | - |
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| terrapin | (noun) any of various edible North American web-footed turtles living in fresh or brackish water | - |
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| terreplein | (noun) level space where heavy guns can be mounted behind the parapet at the top of a rampart | - |
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| tetrodotoxin | (noun) a powerful neurotoxin found in the ovaries of pufferfish | - |
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| theelin | (noun) a naturally occurring weak estrogenic hormone secreted by the mammalian ovary; synthesized (trade name Estronol) and used to treat estrogen deficiency | Synonyms: estrone, Estronol, oestrone |
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| theremin | (noun) an electronic musical instrument; melodies can be played by moving the right hand between two rods that serve as antennas to control pitch; the left hand controls phrasing | - |
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| thiamin | (noun) a B vitamin that prevents beriberi; maintains appetite and growth | Synonyms: aneurin, antiberiberi factor, thiamine, vitamin B1 |
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| tholepin | (noun) a holder attached to the gunwale of a boat that holds the oar in place and acts as a fulcrum for rowing | Synonyms: oarlock, peg, pin, rowlock, thole |
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| threadfin | (noun) mullet-like tropical marine fishes having pectoral fins with long threadlike rays | - |
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| thrombin | (noun) an enzyme that acts on fibrinogen in blood causing it to clot | - |
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| thromboplastin | (noun) an enzyme liberated from blood platelets that converts prothrombin into thrombin as blood starts to clot | Synonyms: factor III, thrombokinase |
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| thymosin | (noun) hormone secreted by the thymus; stimulates immunological activity of lymphoid tissue | - |
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| thyrocalcitonin | (noun) thyroid hormone that tends to lower the level of calcium in the blood plasma and inhibit resorption of bone | Synonyms: calcitonin |
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| thyroglobulin | (noun) an iodine containing protein that is obtained from the thyroid gland and exhibits the general properties of the globulins | - |
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| thyroprotein | (noun) a preparation made from iodinated protein and having an action similar to thyroxine | - |
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| thyrotrophin | (noun) anterior pituitary hormone that stimulates the function of the thyroid gland | Synonyms: thyroid-stimulating hormone, thyrotrophic hormone, thyrotropic hormone, thyrotropin, TSH |
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