nine vs digit

nine and digit both are nouns.

Word	Noun	Adjective	Verb	Adverb
nine	Yes	Yes	No	No
digit	Yes	No	No	No

As nouns, digit is a hypernym of nine; that is, digit is a word with a broader meaning than nine:

Other hypernyms of nine include figure.

nine (noun)	digit (noun)
one of four playing cards in a deck with nine pips on the face	a finger or toe in human beings or corresponding body part in other vertebrates
a team of professional baseball players who play and travel together	one of the elements that collectively form a system of numeration
the cardinal number that is the sum of eight and one	the length of breadth of a finger used as a linear measure

nine (adjective)	digit (adjective)
denoting a quantity consisting of one more than eight and one less than ten