couple vs duo

couple and duo both are nouns.

Word	Noun	Adjective	Verb	Adverb
couple	Yes	No	Yes	No
duo	Yes	No	No	No

As nouns, couple and duo are synonyms defined as:

Other synonyms of couple include duet, twosome.

As nouns, couple and duo are synonyms defined as:

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

couple (noun)	duo (noun)
a pair who associate with one another	a musical composition for two performers
a pair of people who live together	a pair who associate with one another
(physics) something joined by two equal and opposite forces that act along parallel lines	two performers or singers who perform together
two items of the same kind	two items of the same kind
a small indefinite number

couple (verb)	duo (verb)
engage in sexual intercourse
link together
bring two objects, ideas, or people together
form a pair or pairs