billionth vs ordinal

billionth and ordinal both are nouns.

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

billionth (noun)	ordinal (noun)
one part in a billion equal parts	the number designating place in an ordered sequence
position 1,000,000,000 in a countable series of things

billionth (adjective)	ordinal (adjective)
the ordinal number of one billion in counting order	being or denoting a numerical order in a series
	of or relating to a taxonomic order