\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\, 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.