1 vs digit

1 and digit both are nouns.

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

As nouns, digit is a hypernym of 1; that is, digit is a word with a broader meaning than 1:

Other hypernyms of 1 include figure.

1 (noun)	digit (noun)
the smallest whole number or a numeral representing this number	a finger or toe in human beings or corresponding body part in other vertebrates
	one of the elements that collectively form a system of numeration
	the length of breadth of a finger used as a linear measure

1 (adjective)	digit (adjective)
used of a single unit or thing; not two or more