unison

From Middle English unisoun, from Middle French unisson, from Medieval Latin ūnisonus (“having the same sound”), from ūni- +‎ sonus (“sound”).

unison (usually uncountable, plural unisons)

(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.
- 2007 July 16, James R. Oestreich, “With Levine as Tour Guide, a Journey Through Mahler’s Third Symphony”, in New York Times‎:
  The young principal timpanist, Timothy Genis, was superb throughout, though his sidekick timpanist sometimes lagged in the final unisons.
(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.
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.
(by extension) Two or more voices speaking or singing the same words together.

the state of being together, in harmony, at the same time

music: the simultaneous playing of an identical note more than once

Afrikaans: unisoon
Bulgarian: съзвучие (bg) n (sǎzvučie)
Chinese:
Mandarin: 同音 (zh) (tóngyīn), 齐唱 (zh) (qíchàng), 齊唱 / 齐唱 (zh) (qíchàng), 齐奏 (zh) (qízòu), 齊奏 / 齐奏 (zh) (qízòu)
French: unisson (fr) m
German: Unisono n, Einklang (de) m
Irish: comh-airde f, aoncheol m, aontacht f
Italian: unisono (it) m
Japanese: 同音 (ja) (dōon), ユニゾン (yunizon), 斉唱 (ja) (seishō), 斉奏 (ja) (seisō)
Polish: unisono (pl) n
Romanian: primă (ro) f, unison (ro) n
Russian: унисо́н (ru) m (unisón)
Serbo-Croatian: prima (sh) f
Swedish: samråd (sv) c

English