octonary vs octad

octonary and octad both are nouns.

Word	Noun	Adjective	Verb	Adverb
octonary	Yes	No	No	No
octad	Yes	No	No	No

As nouns, octonary and octad are synonyms defined as:

octonary and octad: the cardinal number that is the sum of seven and one

Other synonyms of octonary include 8, eight, eighter, eighter from Decatur, octet, ogdoad, VIII.

octonary (noun)	octad (noun)
the cardinal number that is the sum of seven and one	the cardinal number that is the sum of seven and one