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English definition of “knock”

knock

verb (MAKE NOISE)    /nɒk/ US  /nɑːk/
B1 [I] to repeatedly hit something, producing a noise: She knocked on the window to attract his attention. There's someone knocking on/at the door. Please knock before entering.Hitting against objects accidentally and colliding [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.Sounds made by objects, movement or impact [I] If something such as a pipe knocks, it makes a repeated high sound.Sounds made by objects, movement or impact
(Definition of knock verb (MAKE NOISE) from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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