knock knock /ˈnɑːk/

noun

1. () The sound of knocking (as on a door or in an engine or bearing)  ( knocking , knock )
   the sound of knocking (as on a door or in an engine or bearing)
    The knocking grew louder
   the knocking grew louder
   
2. () Negative criticism  ( roast [Informal] , knock )
   negative criticism
   
3. The act of hitting vigorously  ( belt [Informal] , knock , rap , whack [Informal] , whang [Informal] )
   the act of hitting vigorously
    He gave the table a whack
   he gave the table a whack
   
4. A bad experience  ( knock )
   a bad experience
    The school of hard knocks
   the school of hard knocks
   
5. A vigorous blow  ( knock , bash [Informal] , belt [Informal] , bang , smash )
   a vigorous blow
    The sudden knock floored him
   the sudden knock floored him
    He took a bash right in his face
   he took a bash right in his face
    He got a bang on the head
   he got a bang on the head
   

verb

1. () Deliver a sharp blow or push  ( strike hard , knock )
   deliver a sharp blow or push
    He knocked the glass clear across the room
   He knocked the glass clear across the room
   
2. () Rap with the knuckles  ( knock )
   rap with the knuckles
    Knock on the door
   knock on the door
   
3. () Knock against with force or violence  ( bump , knock )
   knock against with force or violence
    My car bumped into the tree
   My car bumped into the tree
   
4. [Informal] Find fault with; express criticism of; point out real or perceived flaws  ( knock [Informal] , pick apart , criticise [British] , criticize )
   find fault with; express criticism of; point out real or perceived flaws
    The paper criticized the new movie
   The paper criticized the new movie
    Don't knock the food--it's free
   Don't knock the food--it's free
   
5. Sound like a car engine that is firing too early  ( knock , ping , pink )
   sound like a car engine that is firing too early
    The car pinged when I put in low-octane gasoline
   the car pinged when I put in low-octane gasoline
    The car pinked when the ignition was too far retarded
   The car pinked when the ignition was too far retarded
   
6. Make light, repeated taps on a surface  ( knock , pink , rap , tap )
   make light, repeated taps on a surface
    He was tapping his fingers on the table impatiently
   he was tapping his fingers on the table impatiently