B1 [ I ] to repeatedly hit something, producing a noise(反复地)敲,击,打
[ I ] specialized engineering If an engine is knocking, it is producing a repeated high sound either because the fuel is not burning correctly or because a small part is damaged and is therefore allowing another part to move in ways that it should not.(发动机)发爆震声,砰砰作响
[ I ] If something such as a pipe knocks, it makes a repeated high sound.(管子等)发碰撞声
More examples
I wish he'd knock instead of just barging in.
He knocked quietly before entering the room.
She knocked on the table to get our attention.
She never knocks before she comes in.
Knock three times, then I'll know it's you.
B1 [ I + adv/prep, T ] to hit, especially forcefully, and cause to move or fall碰,撞;碰倒;撞倒
If you knock two rooms into each other or knock two rooms through, you remove the wall between them so that they form one room.把(两个房间)打通
More examples
The force of the wind knocked my hat off.
I knocked over a cup of tea.
The chair knocked against the lamp.
She knocked her head on the cupboard door.
Mind you don't knock the glass over.
[ T ] UK informal to criticize, especially unfairly指摘;挑剔
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