| tellurium | (noun) a brittle silver-white metalloid element that is related to selenium and sulfur; it is used in alloys and as a semiconductor; occurs mainly as tellurides in ores of copper and nickel and silver and gold | Synonyms: atomic number 52, Te |
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| tentorium | (noun) (anatomy) a fold of dura mater that covers the cerebellum and supports the occipital lobes of the cerebrum | - |
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| terbium | (noun) a metallic element of the rare earth group; used in lasers; occurs in apatite and monazite and xenotime and ytterbite | Synonyms: atomic number 65, Tb |
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| terrarium | (noun) a vivarium in which selected living plants are kept and observed | - |
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| tetrasporangium | (noun) a sporangium containing four asexual spores | - |
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| thallium | (noun) a soft grey malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores | Synonyms: atomic number 81, Tl |
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| thorium | (noun) a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands | Synonyms: atomic number 90, Th |
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| thrum | (noun) a thrumming sound | - |
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| (verb) make a rhythmic sound | Synonyms: beat, drum |
| (verb) sound with a monotonous hum | Synonyms: hum |
| (verb) sound the strings of (a stringed instrument) | Synonyms: strum |
| thulium | (noun) a soft silvery metallic element of the rare earth group; isotope 170 emits X-rays and is used in small portable X-ray machines; it occurs in monazite and apatite and xenotime | Synonyms: atomic number 69, Tm |
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| titanium | (noun) a light strong grey lustrous corrosion-resistant metallic element used in strong lightweight alloys (as for airplane parts); the main sources are rutile and ilmenite | Synonyms: atomic number 22, Ti |
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| tomentum | (noun) a network of tiny blood vessels between the cerebral surface of the pia mater and the cerebral cortex | Synonyms: tomentum cerebri |
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| (noun) filamentous hairlike growth on a plant | Synonyms: fuzz, hair |
| trapezium | (noun) the wrist bone on the thumb side of the hand that articulates with the 1st and 2nd metacarpals | Synonyms: os trapezium, trapezium bone |
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| (noun) a quadrilateral with no parallel sides | - |
| trichodesmium | (noun) large colonial bacterium common in tropical open-ocean waters; important in carbon and nitrogen fixation | - |
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| triclinium | (noun) a dining table with couches along three sides in ancient Rome | - |
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| (noun) a dining room (especially a dining room containing a dining table with couches along three sides) | - |
| trillium | (noun) any liliaceous plant of the genus Trillium having a whorl of three leaves at the top of the stem with a single three-petaled flower | Synonyms: wake-robin, wood lily |
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| tritium | (noun) a radioactive isotope of hydrogen; atoms of tritium have three times the mass of ordinary hydrogen atoms | - |
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| trivium | (noun) (Middle Ages) an introductory curriculum at a medieval university involving grammar and logic and rhetoric; considered to be a triple way to eloquence | - |
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| tum | (noun) an enlarged and muscular saclike organ of the alimentary canal; the principal organ of digestion | Synonyms: breadbasket, stomach, tummy |
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| tympanum | (noun) a large hemispherical brass or copper percussion instrument with a drumhead that can be tuned by adjusting the tension on it | Synonyms: kettle, kettledrum, timpani, tympani |
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| (noun) the membrane in the ear that vibrates to sound | Synonyms: eardrum, myringa, tympanic membrane |
| (noun) the main cavity of the ear; between the eardrum and the inner ear | Synonyms: middle ear, tympanic cavity |
| ultimatum | (noun) a final peremptory demand | - |
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| unnilquadium | (noun) a radioactive transuranic element which has been synthesized | Synonyms: atomic number 104, element 104, Rf, rutherfordium, Unq |
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| ununbium | (noun) a radioactive transuranic element, with atomic number 112 | Synonyms: atomic number 112, element 112, Uub |
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| ununhexium | (noun) a radioactive transuranic element, with atomic number 116 | Synonyms: atomic number 116, element 116, Uuh |
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| ununpentium | (noun) a radioactive transuranic element, with atomic number 115 | Synonyms: atomic number 115, element 115, Uup |
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| ununquadium | (noun) a radioactive transuranic element, with atomic number 114 | Synonyms: atomic number 114, element 114, Uuq |
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| ununtrium | (noun) a radioactive transuranic element, with atomic number 113 | Synonyms: atomic number 113, element 113, Uut |
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| uranium | (noun) a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons | Synonyms: atomic number 92, U |
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| uropygium | (noun) posterior part of a bird's body from which the tail feathers grow | - |
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| vaccinum | (noun) immunogen consisting of a suspension of weakened or dead pathogenic cells injected in order to stimulate the production of antibodies | Synonyms: vaccine |
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| vacuum | (noun) an electrical home appliance that cleans by suction | Synonyms: vacuum cleaner |
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| (noun) a region that is devoid of matter | Synonyms: vacuity |
| (noun) an empty area or space | Synonyms: emptiness, vacancy, void |
| (noun) the absence of matter | Synonyms: vacuity |
| (verb) clean with a vacuum cleaner | Synonyms: hoover, vacuum-clean |
| vanadium | (noun) a soft silvery white toxic metallic element used in steel alloys; it occurs in several complex minerals including carnotite and vanadinite | Synonyms: atomic number 23, V |
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| variorum | (noun) an edition containing various versions of a text or notes by various scholars or editors | Synonyms: variorum edition |
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| vellum | (noun) fine parchment prepared from the skin of a young animal e.g. a calf or lamb | - |
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| (noun) a heavy creamy-colored paper resembling parchment | - |
| velum | (noun) a muscular flap that closes off the nasopharynx during swallowing or speaking | Synonyms: soft palate |
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| (noun) a membranous covering attached to the immature fruiting body of certain mushrooms | Synonyms: veil |
| verticillium | (noun) a fungus of the genus Verticillium | - |
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| vitellarium | (noun) A modified part of the ovary that in many flatworms and rotifers produces yolk-filled cells serving to nourish the true eggs. | - |
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| vivarium | (noun) an indoor enclosure for keeping and raising living animals and plants and observing them under natural conditions | - |
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| wampum | (noun) small cylindrical beads made from polished shells and fashioned into strings or belts; used by certain Native American peoples as jewelry or currency | Synonyms: peag, wampumpeag |
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| (noun) informal terms for money | Synonyms: boodle, bread, cabbage, clams, dinero, dough, gelt, kale, lettuce, lolly, loot, lucre, moolah, pelf, scratch, shekels, simoleons, sugar |
| whatchamacallum | (noun) something unspecified whose name is either forgotten or not known | Synonyms: dojigger, doodad, doohickey, gimmick, gismo, gizmo, gubbins, thingamabob, thingamajig, thingmabob, thingmajig, thingumabob, thingumajig, thingummy, whatchamacallit, whatsis, widget |
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| xeranthemum | (noun) any plant of the genus Xeranthemum native to southern Europe having chaffy or silvery flower heads with purplish tubular flowers | - |
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| ytterbium | (noun) a soft silvery metallic element; a rare earth of the lanthanide series; it occurs in gadolinite and monazite and xenotime | Synonyms: atomic number 70, Yb |
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| yttrium | (noun) a silvery metallic element that is common in rare-earth minerals; used in magnesium and aluminum alloys | Synonyms: atomic number 39, Y |
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| zirconium | (noun) a lustrous grey strong metallic element resembling titanium; it is used in nuclear reactors as a neutron absorber; it occurs in baddeleyite but is obtained chiefly from zircon | Synonyms: atomic number 40, Zr |
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| zoarium | (noun) a colony of zooids. | - |
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