t

from The American Heritage® Dictionary of the English Language, 5th Edition.

• abbreviation teaspoon
• abbreviation teaspoonful
• abbreviation top quark
• noun The 20th letter of the modern English alphabet.
• noun Any of the speech sounds represented by the letter t.
• noun The 20th in a series.
• noun Something shaped like the letter T.
• idiom (to a T) Perfectly; precisely.

from The Century Dictionary.

• noun A white clay pipe with the initials T. D. on the bowl. Said to be due to a legacy left by the eccentric “Lord” Timothy Dexter of Newburyport, Mass., in order to perpetuate his name. By extension, T. D. means clay pipe. Dialect Notes, III. iii.
• An abbreviation of territory, Testament, Thursday, Titus (a book of the New Testament), Tuesday, Turkish; in medicine, of tension of the eyeball; [lowercase] of tome, ton, town, township, transitive, tun, tungsten, and of the Latin tempore, in the time (of).
• noun An abbreviation of till forbidden.
• noun An abbreviation of till sale.
• noun Something made or fashioned in the form of a T, as a piece of metallic pipe for joining two lines of piping at right angles to each other. Also written tee, and sometimes tau. See T-bandage, T-beard, T-bone, T-cloth, T-iron, T-joint, T-rail, T-square.
• The twentieth letter and sixteenth consonant of the English alphabet.
• The value of the sign has been practically the same through the whole history of its use; it denotes the surd (or breathed) mute (or check) produced by a complete closure (with following breach or explosion) between the tip of the tongue and a point on the roof of the mouth either close behind or not far from the bases of the upper front teeth. Its corresponding sonant or voiced mute is d, and its nasal is n (see these letters). They are oftenest called dental or teeth-sounds, though the teeth have really no part in their production; hence also, and better, lingual, or front lingual, or tongue-tip, etc. They are much more common elements of our utterance than either of the other two classes, palatal (k, g, ng) or labial (p, b, m); they constitute, namely, about 18 per cent. of the sounds we make (t nearly 6 per cent., d nearly 5, n nearly 7), against palatal 4 per cent., and labial 6½. A sound which our ears would at once recognize and name as a t-sound is producible in other positions of the organs than that described above—namely, at points further back on the roof of the mouth, and with parts of the tongue behind the tip, and even of its under surface. Hence the occurrence in some languages of more than one t, distinctly recognized as separate members of the spoken alphabet (so two in Sanskrit, etc., and even four in Siamese); our own t also which forms the first part of the compound ch (= tsh) is slightly but constantly different from our t elsewhere. As in many other languages (and partly by direct inheritance from French, and even from later Latin, alterations), the t in English shows a tendency to become palatalized and converted into a sibilant when followed by palatal sounds, as i, e, y. Hence, in many situations, it combines with such sounds, either regularly or in rapid utterance, producing the ch-sound, as in question, mixture (compare the corresponding conversion of s to sh, under S); and even, in a great number of words having the endings -tion, -tious, -tial, etc., it becomes a sibilant and makes the sh-sound, as in nation, factious, partial, etc. T also, like others of our consonants, frequently occurs double, especially when medial: thus (from fit) fitted, fitter, fitting. With h, t forms the digraph th, which has the position and importance of a fully independent element in the alphabet, with a double pronunciation, surd and sonant (or breathed and voiced): surd in thin, breath; sonant in this, breathe—both as strictly unitary sounds as t and d, or s and z. They are related with t and s, etc., as tongue-tip sounds, especially with s and z as being fricative and continuable; but they are of closer position than the latter, the closest that can be made without actual stoppage of the breath, and are usually formed with the tongue thrust further forward, against or even beyond the teeth: hence their substitution for s and z by persons who lisp. In regard to their grade of closure, they are akin to f and v, and belong in one class with these (oftenest and best called spirants). As an f comes in part from an aspirated p, or ph, so also the th-sounds from an aspirated t; and in this way they have obtained their usual representation: the Greek θ, which was an aspirated t (that is, a t with separately audible h after it), was written in Latin with th, and then, when the aspirate came to be pronounced as a spirant, this was continued in use as representative of the latter. And in this case the Latin digraph has crowded out of English use the sign (or rather the two signs) which in Anglo-Saxon represented the th-sounds—namely, þ, ð—much to the detriment of our present alphabet. Of the two th-sounds, the sonant (or this and breathe sound) is much the more frequent owing chiefly to the constant recurrence of the pronominal words, particularly the, in which it is found; it is nearly 4 per cent. of our utterance, while the surd (or thin and breath sound) is less than two thirds of one per cent. In the phonetic history of the Germanic part of our language, t regularly and usually (when special causes do not prevent) comes from an older d; and, on the other hand, th from an older t: examples for t are two corresponding with duo, eat with ad or ed; for th, thou = tu, three = tri, beareth = fert; for both together, that = tad, tooth = dent.
• As a medieval numeral, 160; with a line over it (T), 160,000.
• An abbreviation: [lowercase] In musical notation, of tenor, tempo (as a t., a tempo), tutti, and tasto (as t. s., tasto solo).
• [lowercase] In a ship's log-book, of thunder
• [lowercase] In zoology, of typacanthid.
• In mathematics: [lowercase] of time; of tensor, a functional symbol.
• noun A symbol suggested by von Behring for a principle alleged to be present in the tubercle bacillus which exerts a catalytic and zymogenic action.
• An abbreviation of Thrice Illustrious.
• noun An abbreviation of topographical engineer.
• noun An abbreviation of the Latin tinctura opii, tincture of opium; of turn over; of Topographical Office (of the Ordnance Survey England). In the last sense also written T-O.
• noun A form of -ed, -ed, in certain words. See -ed, -ed.
• noun An abbreviation of type genus.
• An abbreviation of tasto solo.

from the GNU version of the Collaborative International Dictionary of English.

• the twentieth letter of the English alphabet, is a nonvocal consonant. With the letter h it forms the digraph th, which has two distinct sounds, as in thin, then. See Guide to Pronunciation, §§262-264, and also §§153, 156, 169, 172, 176, 178-180.
• (Surg.) a bandage shaped like the letter T, and used principally for application to the groin, or perineum.
• a kind of fashionable two seated wagon for pleasure driving.
• Iron in bars, having a cross section formed like the letter T, -- used in structures.
• a kind of rail for railroad tracks, having no flange at the bottom so that a section resembles the letter T.
• a ruler having a crosspiece or head at one end, for the purpose of making parallel lines; -- so called from its shape. It is laid on a drawing board and guided by the crosspiece, which is pressed against the straight edge of the board. Sometimes the head is arranged to be set at different angles.
• [Colloq.] exactly, perfectly.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The twentieth letter of the basic modern Latin alphabet.
• noun voiceless alveolar plosive.
• noun mathematics, physics time
• noun tonne
• noun programming (LISP) The atom representing true, as opposed to nil.
• noun The twentieth letter of the English alphabet, called tee and written in the Latin script.
• noun The ordinal number twentieth, derived from this letter of the English alphabet, called tee and written in the Latin script.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a unit of weight equivalent to 1000 kilograms
• noun thyroid hormone similar to thyroxine but with one less iodine atom per molecule and produced in smaller quantity; exerts the same biological effects as thyroxine but is more potent and briefer
• noun one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)
• noun the 20th letter of the Roman alphabet
• noun a base found in DNA (but not in RNA) and derived from pyrimidine; pairs with adenine
• noun hormone produced by the thyroid glands to regulate metabolism by controlling the rate of oxidation in cells