octad vs octonary

octad and octonary both are nouns.

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

As nouns, octad and octonary are synonyms defined as:

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

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

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