n. 1. The ordinal number matching the number nine in a series. 2. One of nine equal parts. 3. Music a. A harmonic or melodic interval of an octave and a second. b. The tone at the upper limit of such an interval. c. A chord consisting of a root with its third, seventh, and ninth. [Middle English ninthe, from Old English nigonthe, from nigon, nine; see new in the Appendix of Indo-European roots.] ninth adv. & adj. |
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.