knock in WordNet English dictionary

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

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