Definitions

1. verb

to strike something gently but firmly, typically with the knuckles, in order to attract attention or to test the sound of something

“She knocked on the door to ask if anyone was home.”

2. noun

a sound made by striking something, typically with the knuckles

“I heard a knock at the door and went to answer it.”

3. verb

to bring about or cause something to happen, typically by a series of events or actions

“The economic crisis knocked many people out of work.”