quash
     v 1: 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" [syn: {repress},
           {keep down}, {subdue}, {subjugate}, {reduce}]
     2: declare invalid; "The contract was annulled"; "void a plea"
        [syn: {invalidate}, {annul}, {void}, {avoid}, {nullify}]
        [ant: {validate}]
Source: WordNet® 2.0