sevener vs heptad

sevener and heptad both are nouns.

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

As nouns, sevener and heptad are synonyms defined as:

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

sevener (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