u ‧ ni ‧ son /ˈjuːnəs ə n, ˈjuːnɪs ə n, -z ə n/ BrE AmE noun
[ Date: 1500-1600 ; Language: Old French ; Origin: Medieval Latin unisonus 'having the same sound' , from Latin uni- + sonus 'sound' ]
in unison
a) 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.
b) 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.