septenary vs heptad

septenary and heptad both are nouns.

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

As nouns, septenary and heptad are synonyms defined as:

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

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

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