u·ni·son (ynĭ-sən, -zən)
a. Identity of pitch; the interval of a perfect prime.
b. The combination of parts at the same pitch or in octaves.
2. The action of speaking the same words simultaneously: The children greeted their teacher in unison.
3. Performance of an action at the same time: crew members rowing in unison; pigeons wheeling in unison.
4. Agreement; concord: Their expectations were in unison.
[Middle English, from Old French, from Medieval Latin ūnisonus, in unison, from Late Latin, monotonous : Latin ūni-, uni- + Latin sonus, sound; see swen- in the Appendix of Indo-European roots.]
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