The Collaborative International Dictionary of English v.0.48:

Third \Third\, n.
   1. The quotient of a unit divided by three; one of three
      equal parts into which anything is divided.
      [1913 Webster]

   2. The sixtieth part of a second of time.
      [1913 Webster]

   3. (Mus.) The third tone of the scale; the mediant.
      [1913 Webster]

   4. pl. (Law) The third part of the estate of a deceased
      husband, which, by some local laws, the widow is entitled
      to enjoy during her life.
      [1913 Webster]

   Major third (Mus.), an interval of two tones.

   Minor third (Mus.), an interval of a tone and a half.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Third \Third\ (th[~e]rd), a. [OE. thirde, AS. [thorn]ridda, fr.
   [thorn]r[imac], [thorn]re['o], three; akin to D. derde third,
   G. dritte, Icel. [thorn]ri[eth]i, Goth. [thorn]ridja, L.
   tertius, Gr. tri`tos, Skr. t[.r]t[imac]ya. See Three, and
   cf. Riding a jurisdiction, Tierce.]
   1. Next after the second; coming after two others; -- the
      ordinal of three; as, the third hour in the day. "The
      third night." --Chaucer.
      [1913 Webster]

   2. Constituting or being one of three equal parts into which
      anything is divided; as, the third part of a day.
      [1913 Webster]

   Third estate.
      (a) In England, the commons, or the commonalty, who are
          represented in Parliament by the House of Commons.
      (b) In France, the tiers ['e]tat. See Tiers ['e]tat.

   Third order (R. C. Ch.), an order attached to a monastic
      order, and comprising men and women devoted to a rule of
      pious living, called the third rule, by a simple vow if
      they remain seculars, and by more solemn vows if they
      become regulars. See Tertiary, n., 1.

   Third person (Gram.), the person spoken of. See Person,
      n., 7.

   Third sound. (Mus.) See Third, n., 3.
      [1913 Webster]

WordNet (r) 3.0 (2006):

third
    adv 1: in the third place; "third we must consider unemployment"
           [syn: third, thirdly]
    adj 1: coming next after the second and just before the fourth
           in position [syn: third, 3rd, tertiary]
    n 1: one of three equal parts of a divisible whole; "it contains
         approximately a third of the minimum daily requirement"
         [syn: one-third, third, tierce]
    2: the fielding position of the player on a baseball team who is
       stationed near the third of the bases in the infield
       (counting counterclockwise from home plate); "he is playing
       third" [syn: third base, third]
    3: following the second position in an ordering or series; "a
       distant third"; "he answered the first question willingly,
       the second reluctantly, and the third with resentment"
    4: the musical interval between one note and another three notes
       away from it; "a simple harmony written in major thirds"
    5: the third from the lowest forward ratio gear in the gear box
       of a motor vehicle; "you shouldn't try to start in third
       gear" [syn: third gear, third]
    6: the base that must be touched third by a base runner in
       baseball; "he was cut down on a close play at third" [syn:
       third base, third]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "third":
   consecutive intervals, degree, diapason, diatessaron,
   diatonic interval, diatonic semitone, divide in thirds,
   enharmonic diesis, enharmonic interval, fifth, fourth, half step,
   halftone, interval, irregular, less semitone, melodic interval,
   note, octave, parallel octaves, schlock, schmatte, second,
   semitone, seventh, sixth, step, tertiary, tierce, tone,
   trichotomize, trifurcate, unison interval, whole step