Definition of ninth

• a. - Following the eight and preceding the tenth; coming after eight others.
• a. - Constituting or being one of nine equal parts into which anything is divided.
• n. - The quotient of one divided by nine; one of nine equal parts of a thing; the next after the eighth.
• n. - An interval containing an octave and a second.
• n. - A chord of the dominant seventh with the ninth added.