Done together with agreement and coordination; worked out and agreed upon in advance.
From concert (agreement or coordination), which comes from Italian concertare meaning 'to harmonize.' From Latin com- (together) + certare (to strive). Music uses 'concert' because musicians must harmonize together.
A 'concerted effort' literally means an effort that's harmonized like musicians in a concert—and just like orchestras, a concerted group effort can accomplish way more than individuals.
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