to put down or suppress completely; quell; subdue: to quash a rebellion.
2.
to make void, annul, or set aside (a law, indictment, decision, etc.).
Origin: 1300–50; Middle English quashen to smash, break, overcome, suppress < Old French quasser, in part < Latin quassāre to shake (frequentative of quatere to shake; compare concussion); in part < Late Latin cassāre to annul, derivative of Latin cassus empty, void
"to make void, annul, crush," early 14c., from O.Fr. quasser "to break, smash," from L. quassare "to shatter," frequentative of quatere "to shake" (pp. quassus). Meaning "suppress" is from M.L. quassare "make null and void," from L. cassus "empty, void," influenced by quassare.