- concert (n.) 1660s, "agreement, accord, harmony," from Fr. concert (16c.), from It. concerto "concert, harmony," from concertare "bring into agreement," in L. "to contend, contest, dispute," from com- "with" (see COM- (Cf. com-)) + certare "to contend, strive," frequentative of certus, variant pp. of cernere "separate, decide" (see CRISIS (Cf. crisis)). Before the word entered English, meaning shifted from "to strive against" to "to strive alongside." Sense of "public musical performance" is 1680s. But Klein considers this too much of a stretch and suggests L. concentare "to sing together" (from con- + cantare "to sing") as the source of the Italian word in the musical sense.
Etymology dictionary. 2014.