duet

Short definition from Wiktionary

Noun

1. 1
   A musical composition in two parts, each performed by a single voice (singer, instrument or univoce ensemble).
2. 2
   A song composed for and/or performed by a duo.
3. 3
   A pair or couple, especially one that is harmonious or elegant.

Verb

1. 1
   To perform a duet.
2. 2
   To communicate (warnings, mating calls, etc.) through song.
3. 3
   To perform (sing, play, etc.) as a duet.
4. 4
   (of two people) To say at the same time, to chorus.

Proper noun

1. 1
   A surname.