composition vs sestet

composition and sestet both are nouns.

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

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

composition (noun)	sestet (noun)
the act of creating written works	a musical composition written for six performers
musical creation	a rhythmic group of six lines of verse
something that is created by arranging several things to form a unified whole	a set of six similar things considered as a unit
the way in which someone or something is composed	six 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 five 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