Origin and history of concussion

the modern English word is a merger of two words, both in Middle English as quashen, from two unrelated Latin verbs.

1. "to suppress, overcome" (mid-13c.); "to make void, annul, nullify, veto" (mid-14c.), from Old French quasser, quassier, casser "to annul, declare void," and directly from Medieval Latin quassare, alteration of Late Latin cassare, from cassus "null, void, empty" (according to Watkins from extended form of PIE root *kes- "to cut"). The meaning "subdue, put down summarily" is from c. 1600.

2. "to break, crush, beat to pieces" early 14c., from Old French quasser, casser "to break, smash, destroy; maltreat, injure, harm, weaken," from Latin quassare "to shatter, shake or toss violently," frequentative of quatere (past participle quassus) "to shake." According to Watkins this is from PIE root *kwet- "to shake" (source also of Greek passein "to sprinkle," Lithuanian kutėti "to shake up," Old Saxon skuddian "to move violently," German schütteln "to shake," Old English scudan "to hasten").

In Medieval Latin, quassare often was used for cassare, and in later French the form of both words is casser. The words in English now are somewhat, or entirely, fused. Related: Quashed; quashing.

1590s, "to shake violently" (the original sense is now rare or obsolete), from Latin concuss-, past-participle stem of concutere "to dash together, shake violently" (see concussion). The meaning "give a concussion to the brain" is from 1680s. Related: Concussed; concussing.