The noun knock has 5 senses (first 2 from tagged texts)
1. (2) knock, knocking -- (the sound of knocking (as on a door or in an engine or bearing); "the knocking grew louder")
2. (1) knock, roast -- (negative criticism)
3. knock, bash, bang, smash, belt -- (a vigorous blow; "the sudden knock floored him"; "he took a bash right in his face"; "he got a bang on the head")
4. knock -- (a bad experience; "the school of hard knocks")
5. knock, belt, rap, whack, whang -- (the act of hitting vigorously; "he gave the table a whack")
Overview of verb knock
The verb knock has 6 senses (first 3 from tagged texts)
1. (7) knock, strike hard -- (deliver a sharp blow or push :"He knocked the glass clear across the room")
2. (6) knock -- (rap with the knuckles; "knock on the door")
3. (4) bump, knock -- (knock against with force or violence; "My car bumped into the tree")
4. tap, rap, knock, pink -- (make light, repeated taps on a surface; "he was tapping his fingers on the table impatiently")
5. pink, ping, knock -- (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")
6. knock, criticize, criticise, pick apart -- (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")