eighteenth vs ordinal

eighteenth and ordinal both are nouns.

Word	Noun	Adjective	Verb	Adverb
eighteenth	Yes	Yes	No	No
ordinal	Yes	Yes	No	No

eighteenth (noun)	ordinal (noun)
position 18 in a countable series of things	the number designating place in an ordered sequence

eighteenth (adjective)	ordinal (adjective)
coming next after the seventeenth in position	being or denoting a numerical order in a series
	of or relating to a taxonomic order