twenty-first vs ordinal

twenty-first is not a noun while ordinal is a noun.

Word	Noun	Adjective	Verb	Adverb
twenty-first	No	Yes	No	No
ordinal	Yes	Yes	No	No

twenty-first (noun)	ordinal (noun)
	the number designating place in an ordered sequence

twenty-first (adjective)	ordinal (adjective)
coming next after the twentieth in position	being or denoting a numerical order in a series
	of or relating to a taxonomic order