The Collaborative International Dictionary of English v.0.48:

Mute \Mute\, n.
   1. One who does not speak, whether from physical inability,
      unwillingness, or other cause. Specifically:
      (a) One who, from deafness, either congenital or from
          early life, is unable to use articulate language; a
          deaf-mute.
      (b) A person employed by undertakers at a funeral.
      (c) A person whose part in a play does not require him to
          speak.
      (d) Among the Turks, an officer or attendant who is
          selected for his place because he can not speak.
          [1913 Webster]

   2. (Phon.) A letter which represents no sound; a silent
      letter; also, a close articulation; an element of speech
      formed by a position of the mouth organs which stops the
      passage of the breath; as, p, b, d, k, t.
      [1913 Webster]

   3. (Mus.) A little utensil made of brass, ivory, or other
      material, so formed that it can be fixed in an erect
      position on the bridge of a violin, or similar instrument,
      in order to deaden or soften the tone.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

T \T\ (t[=e]),
   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, [sect][sect]262-264, and also [sect][sect]153,
   156, 169, 172, 176, 178-180.
   [1913 Webster] The letter derives its name and form from the
   Latin, the form of the Latin letter being further derived
   through the Greek from the Ph[oe]nician. The ultimate origin
   is probably Egyptian. It is etymologically most nearly
   related to d, s, th; as in tug, duke; two, dual, L. duo;
   resin, L. resina, Gr. "rhti`nh, tent, tense, a., tenuous,
   thin; nostril, thrill. See D, S.
   [1913 Webster]

   T bandage (Surg.), a bandage shaped like the letter T, and
      used principally for application to the groin, or
      perineum.

   T cart, a kind of fashionable two seated wagon for pleasure
      driving.

   T iron.
   (a) A rod with a short crosspiece at the end, -- used as a
       hook.
   (b) Iron in bars, having a cross section formed like the
       letter T, -- used in structures.

   T rail, a kind of rail for railroad tracks, having no
      flange at the bottom so that a section resembles the
      letter T.

   T square, 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.

   To a T, exactly, perfectly; as, to suit to a T. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

T
    n 1: a base found in DNA (but not in RNA) and derived from
         pyrimidine; pairs with adenine [syn: thymine, T]
    2: one of the four nucleotides used in building DNA; all four
       nucleotides have a common phosphate group and a sugar
       (ribose) [syn: deoxythymidine monophosphate, T]
    3: a unit of weight equivalent to 1000 kilograms [syn: metric
       ton, MT, tonne, t]
    4: the 20th letter of the Roman alphabet [syn: T, t]
    5: 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 [syn: triiodothyronine, liothyronine, T]
    6: hormone produced by the thyroid glands to regulate metabolism
       by controlling the rate of oxidation in cells; "thyroxine is
       65% iodine" [syn: thyroxine, thyroxin,
       tetraiodothyronine, T]

The Jargon File (version 4.4.7, 29 Dec 2003):

T
 /T/

    1. [from LISP terminology for ?true?] Yes. Used in reply to a question
    (particularly one asked using The -P convention). In LISP, the constant T
    means ?true?, among other things. Some Lisp hackers use ?T? and ?NIL?
    instead of ?Yes? and ?No? almost reflexively. This sometimes causes
    misunderstandings. When a waiter or flight attendant asks whether a hacker
    wants coffee, he may absently respond ?T?, meaning that he wants coffee;
    but of course he will be brought a cup of tea instead. Fortunately, most
    hackers (particularly those who frequent Chinese restaurants) like tea at
    least as well as coffee ? so it is not that big a problem.

    2. See time T (also since time T equals minus infinity).

    3. [techspeak] In transaction-processing circles, an abbreviation for the
    noun ?transaction?.

    4. [Purdue] Alternate spelling of tee.

    5. A dialect of LISP developed at Yale. (There is an intended allusion to
    NIL, ?New Implementation of Lisp?, another dialect of Lisp developed for
    the VAX)


The Free On-line Dictionary of Computing (30 December 2018):

T
T Lisp

   1. True.  A Lisp compiler by Johnathan A. Rees in 1982 at
   Yale University.  T has static scope and is a
   near-superset of Scheme.  Unix source is available.  T is
   written in itself and compiles to efficient native code.  Used
   as the basis for the Yale Haskell system.  Maintained by
   David Kranz .

   (ftp://ftp.ai.mit.edu/pub/systems/t3.1).

   A multiprocessing version of T is available
   (ftp://masala.lcs.mit.edu/pub/mult).

   Runs on Decstation, SPARC, Sun-3, Vax under Unix,
   Encore, HP, Apollo, Macintosh under A/UX.

   E-mail:  (bugs).
   E-mail: .

   (1991-11-26)

   ["The T Manual", Johnathan A. Rees  et
   al, Yale U, 1984].

   2. A functional language.

   ["T: A Simple Reduction Language Based on Combinatory Term
   Rewriting", Ida et al, Proc of Prog Future Generation
   Computers, 1988].

   3. (lower case) The Lisp atom used to represent "true",
   among other things.  "false" is represented using the same
   atom as an empty list, nil.  This overloading of the basic
   constants of the language helps to make Lisp write-only
   code.

   4. In transaction-processing circles, an abbreviation for
   "transaction".

   5. (Purdue) An alternative spelling of "tee".


The Devil's Dictionary (1881-1906):

T, the twentieth letter of the English alphabet, was by the Greeks
absurdly called _tau_.  In the alphabet whence ours comes it had the
form of the rude corkscrew of the period, and when it stood alone
(which was more than the Phoenicians could always do) signified
_Tallegal_, translated by the learned Dr. Brownrigg, "tanglefoot."