three vs digit

three and digit both are nouns.

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

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

Other hypernyms of three include figure.

three (noun)	digit (noun)
one of four playing cards in a deck having three pips	a finger or toe in human beings or corresponding body part in other vertebrates
the cardinal number that is the sum of one and one and one	one of the elements that collectively form a system of numeration
	the length of breadth of a finger used as a linear measure

three (adjective)	digit (adjective)
being one more than two