heptad vs digit

heptad and digit both are nouns.

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

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

Other hypernyms of heptad include figure.

heptad (noun)	digit (noun)
the cardinal number that is the sum of six and one	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