octad vs octet

octad and octet both are nouns.

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

As nouns, octad and octet are synonyms defined as:

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

octad (noun)	octet (noun)
the cardinal number that is the sum of seven and one	a musical composition written for eight performers
	eight people considered as a unit
	a set of eight similar things considered as a unit
	eight performers or singers who perform together
	the cardinal number that is the sum of seven and one