knock

knock (http://definr.com/knock)

     n 1: the sound of knocking (as on a door or in an engine or
          bearing); "the knocking grew louder" [syn: knocking]
     2: negative criticism [syn: roast]
     3: a vigorous blow; "the sudden knock floored him"; "he took a
        bash right in his face"; "he got a bang on the head" [syn:
         bash, bang, smash, belt]
     4: a bad experience; "the school of hard knocks"
     5: the act of hitting vigorously; "he gave the table a whack"
        [syn: belt, rap, whack, whang]
     v 1: deliver a sharp blow or push :"He knocked the glass clear
          across the room." [syn: strike hard]
     2: rap with the knuckles; "knock on the door"
     3: knock against with force or violence; "My car bumped into
        the tree" [syn: bump]
     4: make light, repeated taps on a surface; "he was tapping his
        fingers on the table impatiently" [syn: tap, rap, pink]
     5: of car engines, when firing too early [syn: ping]