six vs digit

six and digit both are nouns.

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

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

Other hypernyms of six include figure.

six (noun)	digit (noun)
a playing card or domino or die whose upward face shows six pips	a finger or toe in human beings or corresponding body part in other vertebrates
the cardinal number that is the sum of five 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

six (adjective)	digit (adjective)
denoting a quantity consisting of six items or units