quash

verbs

put down by force or intimidation

"The government quashes any attempt of an uprising"; "China keeps down her dissidents very efficiently"; "The rich landowners subjugated the peasants working the land"

keep down, quash, reduce, repress, subdue, subjugate

declare invalid

"The contract was annulled"; "void a plea"

annul, avoid, invalidate, nullify, quash, void