＞concert (n.)
1660s, "agreement of two or more in design or plan; accord, harmony," from French concert (16c.), from Italian concerto "concert, harmony," from concertare "bring into agreement," apparently from Latin concertare "to contend with zealously, contest, dispute, debate" from assimilated form of com "with" (see con-) + certare "to contend, strive," frequentative of certus, variant past participle of cernere "separate, distinguish, decide" (from PIE root *krei- "to sieve," thus "discriminate, distinguish").

The proposed sense evolution between Latin ("to contend with") and medieval Italian ("bring into agreement") seems extreme and is difficult to explain.
(出典　www.etymonline.com/search?q=concert)