ordinal vs 4th

ordinal is a noun but 4th is not a noun.

Word	Noun	Adjective	Verb	Adverb
ordinal	Yes	Yes	No	No
4th	No	Yes	No	No

ordinal (noun)	4th (noun)
the number designating place in an ordered sequence

ordinal (adjective)	4th (adjective)
being or denoting a numerical order in a series	coming next after the third and just before the fifth in position or time or degree or magnitude
of or relating to a taxonomic order