composition vs octet

composition and octet both are nouns.

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

As nouns, octet is a hyponym of composition; that is, octet is a word with a more specific, narrower meaning than composition:

composition (noun)	octet (noun)
the act of creating written works	a musical composition written for eight performers
musical creation	eight people considered as a unit
something that is created by arranging several things to form a unified whole	a set of eight similar things considered as a unit
the way in which someone or something is composed	eight performers or singers who perform together
the spatial property resulting from the arrangement of parts in relation to each other and to the whole	the cardinal number that is the sum of seven and one
an essay (especially one written as an assignment)
a musical work that has been created
art and technique of printing with movable type
a mixture of ingredients