number one vs ordinal number

number one and ordinal number both are nouns.

Word	Noun	Adjective	Verb	Adverb
number one	Yes	No	No	No
ordinal number	Yes	No	No	No

As nouns, ordinal number is a hypernym of number one; that is, ordinal number is a word with a broader meaning than number one:

Other hypernyms of number one include no., ordinal.

number one (noun)	ordinal number (noun)
a reference to yourself or myself etc.; `take care of number one' means to put your own interests first	the number designating place in an ordered sequence
the first element in a countable series
the first or highest in an ordering or series