| thalamus | (noun) large egg-shaped structures of grey matter that form the dorsal subdivision of the diencephalon | - |
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| thallus | (noun) a plant body without true stems or roots or leaves or vascular system; characteristic of the thallophytes | - |
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| thesaurus | (noun) a book containing a classified list of synonyms | Synonyms: synonym finder |
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| thiobacillus | (noun) small rod-shaped bacteria living in sewage or soil and oxidizing sulfur | - |
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| thrombus | (noun) a blood clot formed within a blood vessel and remaining attached to its place of origin | - |
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| thus | (noun) an aromatic gum resin obtained from various Arabian or East African trees; formerly valued for worship and for embalming and fumigation | Synonyms: frankincense, gum olibanum, olibanum |
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| thymus | (noun) a ductless glandular organ at the base of the neck that produces lymphocytes and aids in producing immunity; atrophies with age | Synonyms: thymus gland |
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| thyrsus | (noun) a dense flower cluster (as of the lilac or horse chestnut) in which the main axis is racemose and the branches are cymose | Synonyms: thyrse |
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| tinnitus | (noun) a ringing or booming sensation in one or both ears; a symptom of an ear infection or Meniere's disease | - |
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| tonus | (noun) the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli | Synonyms: tone, tonicity |
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| tophus | (noun) an incrustation that forms on the teeth and gums | Synonyms: calculus, tartar |
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| (noun) a deposit of urates around a joint or in the external ear; diagnostic of advanced or chronic gout | Synonyms: chalkstone |
| torus | (noun) commonly the lowest molding at the base of a column | Synonyms: tore |
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| (noun) a ring-shaped surface generated by rotating a circle around an axis that does not intersect the circle | Synonyms: toroid |
| tragus | (noun) a small cartilaginous flap in front of the external opening of the ear | - |
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| trapezius | (noun) either of two flat triangular muscles of the shoulder and upper back that are involved in moving the shoulders and arms | Synonyms: cowl muscle, musculus trapezius, trapezius muscle |
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| trigeminus | (noun) the main sensory nerve of the face and motor nerve for the muscles of mastication | Synonyms: fifth cranial nerve, nervus trigeminus, trigeminal, trigeminal nerve |
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| trismus | (noun) prolonged spasm of the jaw muscles | - |
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| trolleybus | (noun) a passenger bus with an electric motor that draws power from overhead wires | Synonyms: trackless trolley, trolley coach |
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| tumulus | (noun) (archeology) a heap of earth placed over prehistoric tombs | Synonyms: barrow, burial mound, grave mound |
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| typhus | (noun) rickettsial disease transmitted by body lice and characterized by skin rash and high fever | Synonyms: typhus fever |
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| tyrannosaurus | (noun) large carnivorous bipedal dinosaur having enormous teeth with knifelike serrations; may have been a scavenger rather than an active predator; later Cretaceous period in North America | Synonyms: tyrannosaur, Tyrannosaurus rex |
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| umbilicus | (noun) a scar where the umbilical cord was attached | Synonyms: belly button, bellybutton, navel, omphalos, omphalus |
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| unconscious | (noun) that part of the mind wherein psychic activity takes place of which the person is unaware | Synonyms: unconscious mind |
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| uncus | (noun) (biology) any hook-shaped process or part | - |
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| urus | (noun) large recently extinct long-horned European wild ox; considered one of the ancestors of domestic cattle | Synonyms: aurochs, Bos primigenius |
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| uterus | (noun) a hollow muscular organ in the pelvic cavity of females; contains the developing fetus | Synonyms: womb |
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| utriculus | (noun) a small pouch into which the semicircular canals open | Synonyms: utricle |
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| vaginismus | (noun) muscular contraction that causes the vagina to close; usually an anxiety reaction before coitus or pelvic examination | - |
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| vagus | (noun) a mixed nerve that supplies the pharynx and larynx and lungs and heart and esophagus and stomach and most of the abdominal viscera | Synonyms: nervus vagus, pneumogastric, pneumogastric nerve, tenth cranial nerve, vagus nerve, wandering nerve |
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| valgus | (noun) a deformity in which there is an abnormal displacement of part of a limb away from the midline of the body | - |
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| varus | (noun) a deformity in which part of a limb is turned inward to an abnormal degree | - |
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| ventriculus | (noun) thick-walled muscular pouch below the crop in many birds and reptiles for grinding food | Synonyms: gastric mill, gizzard |
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| vesiculovirus | (noun) an animal virus that causes vesicular stomatitis | - |
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| viaticus | (noun) purchasing insurance policies for cash from terminally ill policy holders | Synonyms: viatication |
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| villus | (noun) a minute hairlike projection on mucous membrane | - |
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| virus | (noun) (virology) ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic; a piece of nucleic acid (DNA or RNA) wrapped in a thin coat of protein | - |
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| (noun) a software program capable of reproducing itself and usually capable of causing great harm to files or other programs on the same computer | Synonyms: computer virus |
| (noun) a harmful or corrupting agency | - |
| viscus | (noun) a main organ that is situated inside the body | Synonyms: internal organ |
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| vitellus | (noun) nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg) | Synonyms: yolk |
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| volvulus | (noun) abnormal twisting of the intestines (usually in the area of the ileum or sigmoid colon) resulting in intestinal obstruction | - |
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| vomitus | (noun) the matter ejected in vomiting | Synonyms: barf, puke, vomit |
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| walrus | (noun) either of two large northern marine mammals having ivory tusks and tough hide over thick blubber | Synonyms: sea horse, seahorse |
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| xerophthalmus | (noun) abnormal dryness of the conjunctiva and cornea of the eyes; may be due to a systemic deficiency of vitamin A | Synonyms: conjunctivitis arida, xeroma, xerophthalmia |
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| yus | (noun) a Common Slavonic nasal vowel in the early Cyrillic and Glagolitic alphabets. | - |
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