(1):

(a.) Constituting or being one of nine equal parts into which anything is divided.

(2):

(n.) The quotient of one divided by nine; one of nine equal parts of a thing; the next after the eighth.

(3):

(a.) Following the eight and preceding the tenth; coming after eight others.

(4):

(n.) A chord of the dominant seventh with the ninth added.

(5):

(n.) An interval containing an octave and a second.