TO KNOCK - [verb] to make a noise by hitting something with your close hand
Examples of use
Somebody's knocking at the door. That'll be the postman.
Children were knocking on the window to annoy their nasty neighbour.
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English speaking practise
Remember that if you don't use that word in English conversations or writing you'll forget it in a short time. So the best thing you can do to learn this word is just trying to use it in speaking or writing. Remember also that practise is the key to fluent english speaking.
You can always find a partner, who would also like to improve his/her