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.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.