Source : Webster's Revised Unabridged Dictionary (1913)

Fifteenth \Fif"teenth`\, a. [OE. fiftenthe; cf. fiftethe, AS.
   f[=i]fte[=o][eth]a. See {Fifteen}.]
   1. Next in order after the fourteenth; -- the ordinal of
      fifteen.

   2. Consisting of one of fifteen equal parts or divisions of a
      thing.

Fifteenth \Fif"teenth`\, n.
   1. One of fifteen equal parts or divisions; the quotient of a
      unit divided by fifteen.

   2. A species of tax upon personal property formerly laid on
      towns, boroughs, etc., in England, being one fifteenth
      part of what the personal property in each town, etc., had
      been valued at. --Burrill.

   3. (Mus.)
      (a) A stop in an organ tuned two octaves above the
          diaposon.
      (b) An interval consisting of two octaves.

Source : WordNet®

fifteenth
     adj : coming next after the fourteenth and just before the
           sixteenth in position [syn: {15th}]
     n : position 15 in a countable series of things