duet vs couplet

duet and couplet both are nouns.

Word	Noun	Adjective	Verb	Adverb
duet	Yes	No	No	No
couplet	Yes	No	No	No

As nouns, duet and couplet are synonyms defined as:

Other synonyms of duet include brace, couple, distich, duad, duo, dyad, pair, span, twain, twosome, yoke.

duet (noun)	couplet (noun)
(ballet) a dance for two people (usually a ballerina and a danseur noble)	a stanza consisting of two successive lines of verse; usually rhymed
a musical composition for two performers	two items of the same kind
a pair who associate with one another
two performers or singers who perform together
two items of the same kind