ninth vs 9th

ninth is a noun but 9th is not a noun.

Word	Noun	Adjective	Verb	Adverb
ninth	Yes	Yes	No	No
9th	No	Yes	No	No

As adjectives, ninth and 9th are synonyms defined as:

ninth and 9th: coming next after the eighth and just before the tenth in position

ninth (noun)	9th (noun)
one part in nine equal parts
position nine in a countable series of things

ninth (adjective)	9th (adjective)
coming next after the eighth and just before the tenth in position	coming next after the eighth and just before the tenth in position