concussion (n.)

c. 1400, "a bruising, contusion (to the head)," from Latin concussionem (nominative concussio) "a shaking, an earthquake," noun of action from past-participle stem of concutere "shake violently," from assimilated form of com "with, together" (see con-) + quatere "to shake" (see quash).

From late 15c. as "act of shaking or agitation," especially by impact of another body; from 1540s as "brain injury caused by a fall or blow."