Source : Webster's Revised Unabridged Dictionary (1913)

Y \Y\ (w[imac]), n.; pl. {Y's} (w[imac]z) or {Ys}.
   Something shaped like the letter Y; a forked piece resembling
   in form the letter Y. Specifically:
   (a) One of the forked holders for supporting the telescope of
       a leveling instrument, or the axis of a theodolite; a
       wye.
   (b) A forked or bifurcated pipe fitting.
   (c) (Railroads) A portion of track consisting of two
       diverging tracks connected by a cross track.

   {Y level} (Surv.), an instrument for measuring differences of
      level by means of a telescope resting in Y's.

   {Y moth} (Zo["o]l.), a handsome European noctuid moth {Plusia
      gamma}) which has a bright, silvery mark, shaped like the
      letter Y, on each of the fore wings. Its larva, which is
      green with five dorsal white species, feeds on the
      cabbage, turnip, bean, etc. Called also {gamma moth}, and
      {silver Y}.

Y \Y\ (w[imac]).
   Y, the twenty-fifth letter of the English alphabet, at the
   beginning of a word or syllable, except when a prefix (see
   Y-), is usually a fricative vocal consonant; as a prefix, and
   usually in the middle or at the end of a syllable, it is a
   vowel. See Guide to Pronunciation, [sect][sect] 145, 178-9,
   272.

   Note: It derives its form from the Latin Y, which is from the
         Greek [Upsilon], originally the same letter as V.
         Etymologically, it is most nearly related to u, i, o,
         and j. g; as in full, fill, AS. fyllan; E. crypt,
         grotto; young, juvenile; day, AS. d[ae]g. See {U}, {I},
         and {J}, {G}.

   Note: Y has been called the Pythagorean letter, because the
         Greek letter [Upsilon] was taken represent the sacred
         triad, formed by the duad proceeding from the monad;
         and also because it represents the dividing of the
         paths of vice and virtue in the development of human
         life.

Y \Y\ ([imac]), pron.
   I. [Obs.] --King Horn. Wyclif.

Source : WordNet®

Y
     n 1: a silvery metallic element that is common in rare-earth
          minerals; used in magnesium and aluminum alloys [syn: {yttrium},
           {atomic number 39}]
     2: the 25th letter of the Roman alphabet

Source : Free On-Line Dictionary of Computing

Y
     
        1. General purpose language syntactically like {RATFOR},
        semantically like {C}.  Lacks structures and pointers.  Used
        as a source language for Jack W. Davidson and Christopher
        W. Fraser's peephole optimiser which inspired {GCC} {RTL} and
        other optimisation ideas.
     
        {(ftp://ftp.cs.princeton.edu/pub/y+po.tar.Z)}.  It is a copy
        of the original distribution from the {University of Arizona}
        during the early 80's, totally unsupported.
     
        ["The Y Programming Language", D.R. Hanson, SIGPLAN Notices
        16(2):59-68 (Feb 1981)].
     
        [Jack W. Davidson and Christopher W. Fraser, "The Design and
        Application of a Retargetable Peephole Optimiser", TOPLAS,
        Apr.  1980].
     
        [Jack W. Davidson, "Simplifying Code Through Peephole
        Optimisation" Technical Report TR81-19, The University of
        Arizona, Tucson, AZ, 1981].
     
        [Jack W. Davidson and Christopher W. Fraser, "Register
        Allocation and Exhaustive Peephole Optimisation"
        Software-Practice and Experience, Sep. 1984].
     
        2. See {fixed point combinator}.