knock

To knock is to hit a surface in a quick way, often to make a sound. You might knock on a door before you go in, or a strong wind might knock over a pile of books. It can also mean beating someone down in a fight, as when a boxer gets "knocked out." In everyday speech, people also say "knock it off" to tell someone to stop doing something annoying.

Think of a detective in a movie: they always knock on doors while investigating. Or imagine building a tower of blocks; one careless move can knock the whole thing down. The phrase "knock on wood" is a common superstition people use after talking about their good luck.

The idea behind knock is simple, but it travels far. At its most basic, it means hitting a surface so it makes a sound, especially a door. That is the everyday, polite use: you knock before entering. But the word also appears in other scenes. Branches can knock against a window in a storm, and an engine can knock when something is wrong inside.

From there, the meaning widens. A person or thing can knock something over, down, or out. A punch can knock a fighter out. A careless step can knock over a vase. In a more figurative way, a shop can knock ten dollars off a price, or a runner can knock a few seconds off a personal record. The word can also mean to criticize, especially in informal speech, as in "Don't knock it till you've tried it."

It also lives in many familiar phrases. To "knock someone's socks off" is to impress them a lot. To "knock yourself out" is a casual way of saying "go ahead." "Knock it off" means stop. So whether it is a light sound at the door, a blow that brings someone down, a small cut in price, or a negative comment, knock is a flexible word built around contact, effect, and sudden change.