knock

a vigorous blow

“the sudden knock floored him”

a bad experience

“the school of hard knocks”

rap with the knuckles

“knock on the door”

the act of hitting vigorously

find fault with; express criticism of; point out real or perceived flaws

“Don't knock the food--it's free”

deliver a sharp blow or push

“He knocked the glass clear across the room”

knock against with force or violence

make light, repeated taps on a surface

the sound of knocking (as on a door or in an engine or bearing)

“the knocking grew louder”

sound like a car engine that is firing too early

negative criticism