An abrupt rapping sound, as from an impact of a hard object against wood.
"The heavy door gave a sharp knock when the ball struck it during practice."
In plain English: A knock is an act of hitting something with your hand to get attention or make noise.
"She heard a gentle knock on the front door while she was in the kitchen."
Usage: Use the noun form when referring specifically to the sharp sound made by striking something, such as hearing a knock at the door before opening it. The verb is appropriate only when describing the physical action of creating that sound or attempting entry.
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"
To strike for admittance; to rap upon, as a door.
"She knocked on the front door three times before anyone answered."
In plain English: To knock means to hit something lightly with your hand, fist, or another object.
"He knocked on the door three times before anyone answered."
A suburb and ward in Belfast, Northern Ireland.
"Knock is a suburban area located on the outskirts of Belfast in Northern Ireland."
The word "knock" comes from Old English cnocian, meaning to pound or beat. It traveled into Middle English as knokken before becoming the modern verb we use today for striking something with a sharp sound.