In unison is a phrase used to describe when two or more people or things are working or moving together simultaneously. There are plenty of synonyms for in unison that can be used to indicate working in harmony like together, simultaneously, concurrently, in concert, all at once, in sync, in cooperation, jointly, in agreement, in parallel, in step, and in harmony. Each of these synonyms has their own unique meaning and can be used depending on the context it is being used in. These synonyms can be used in various scenarios such as singing, dancing, speaking, marching, and many more, where being in sync is crucial.