Any couplet.
A couplet, a two-line stanza making complete sense.
Distichous.
A pair or couple, especially one that is harmonious or elegant.
A musical composition in two parts, each performed by a single voice (singer, instrument or univoce ensemble).
A song composed for and/or performed by a duo.
To perform (sing, play, etc.) as a duet.
(of two people) To say at the same time, to chorus.
To perform a duet.
To communicate (warnings, mating calls, etc.) through song.