ninth 
(nīnth)
(nīnth)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.