9th vs ninth

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

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

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

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

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

9th (adjective)	ninth (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