|Origin:||Medieval Latin unisonus 'having the same sound', from Latin uni- + sonus 'sound'|
if people speak or do something in unison, they say the same words at the same time or do the same thing at the same time:
'Good morning!' the kids replied in unison.
if two groups, governments etc do something in unison, they do it together because they agree with each other:
Management and workers must act in unison to compete with foreign business.