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