knock

Knock is a word with multiple related uses in English. As a verb, it means to strike a surface with a quick, often sharp blow. It can also mean to collide with something or to cause something to produce a sound by striking. As a noun, knock refers to the act of striking itself and to the sound that results from such an impact.

Knock is also used as an onomatopoeia that imitates the sound of a light impact. In everyday language, it is frequently used when someone taps on a door to announce their presence or to get someone’s attention behind a barrier.

Knock-knock jokes are a well-known form of humor that relies on a call-and-response structure and a pun in the final line. They began as a simple children's joke pattern and have persisted in popular culture.

In sports, the term knockout, often abbreviated KO, denotes a fight-ending outcome in which a competitor is rendered unconscious or unable to resume competition after a blow deemed legal by the rules.

Common idioms include knock on wood, a superstition intended to prevent bad luck, and knock someone for a loop, meaning to surprise or overwhelm them. Another expression is to knock something down, meaning to topple or defeat it.