ninth (adj., n.)

"next in order or rank after the eighth; being one of nine equal parts into which a whole is regarded as divided;" c. 1300, nynþe, an alteration or replacement (by influence of nine) of nigonðe, from Old English nigoða, nigend. As a noun, "ordinal numeral corresponding to nine," late 13c. As the name of a musical interval, 1590s. Related: Ninthly.

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Definitions of ninth from WordNet
ninth (n.)
position nine in a countable series of things;
going into the ninth they were a run ahead
ninth (n.)
one part in nine equal parts;
Synonyms: one-ninth
ninth (adj.)
coming next after the eighth and just before the tenth in position;
Synonyms: th