Source : Webster's Revised Unabridged Dictionary (1913)

Ninth \Ninth\, a. [From {Nine}; cf. AS. nigo[eth]a.]
   1. Following the eight and preceding the tenth; coming after
      eight others.

   2. Constituting or being one of nine equal parts into which
      anything is divided.

Ninth \Ninth\, n.
   1. The quotient of one divided by nine; one of nine equal
      parts of a thing; the next after the eighth.

   2. (Mus.)
      (a) An interval containing an octave and a second.
      (b) A chord of the dominant seventh with the ninth added.

Source : WordNet®

ninth
     adj : coming next after the eighth and just before the tenth in
           position [syn: {9th}]

ninth
     n 1: position nine in a countable series of things; "going into
          the ninth they were a run ahead"
     2: a ninth part [syn: {one-ninth}]