quash

(verb) put down by force or intimidation. Synonyms: repress, keep down, subdue, subjugate, reduce. Examples: "The government quashes any attempt of an uprising." "China keeps down her dissidents very efficiently." "The rich landowners subjugated the peasants working the land."

(verb) declare invalid. Synonyms: invalidate, annul, void, avoid, nullify. Examples: "The contract was annulled." "Void a plea."