From Middle English unisoun, from Middle French unisson, from Medieval Latin ūnisonus, from ūni- + sonus.

• IPA: /ˈjunɪsən/, /ˈjunɪzən/

unison (uncountable)

1. (music, acoustics) Identical pitch between two notes or sounds; the simultaneous playing of notes of identical pitch (or separated by one or more octaves). [from 15th c.]

   The unison has a pitch ratio of 1:1.

2. (music, acoustics) A sound or note having the same pitch as another, especially when used as the base note for an interval; a unison string. [from 15th c.]
   • 1751, [Tobias] Smollett, The Adventures of Peregrine Pickle […], volume (please specify |volume=I to IV), London: Harrison and Co., […], →OCLC ↗:

     I could not behold him without emotion; when he accosted me, his well-known voice made my heart vibrate, like a musical chord, when its unison is struck.

3. The state of being in harmony or agreement; harmonious agreement or togetherness, synchronisation. [from 17th c.]

   Everyone moved in unison, but the sudden change in weight distribution capsized the boat.

4. (by extension) Two or more voices speaking or singing the same words together.

• (in music) P1

• German: Einklang, Gleichklang, Eintracht
• Russian: согла́сие

• French: unisson
• German: Unisono, Einklang
• Italian: unisono
• Russian: унисо́н

1. (British, labor union) A public-sector trade union in the United Kingdom.