Source : Webster's Revised Unabridged Dictionary (1913)

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

   2. The sixtieth part of a second of time.

   3. (Mus.) The third tone of the scale; the mediant.

   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.

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

   {Minor third} (Mus.), an interval of a tone and a half.