heptad vs septenary

heptad and septenary both are nouns.

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

As nouns, heptad and septenary are synonyms defined as:

heptad and septenary: the cardinal number that is the sum of six and one

Other synonyms of heptad include 7, septet, seven, sevener, VII.

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