Knock

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Old English cnocian, of imitative origin.

wiktionary

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From Middle English knokken, from Old English cnocian, ġecnocian, cnucian(“to knock, pound on, beat”), from Proto-West Germanic *knokōn, from Proto-Germanic *knukōną(“to knock”), a suffixed form of *knu-, *kneu-(“to pound on, beat”), from Proto-Indo-European *gen-(“to squeeze, pinch, kink, ball up, concentrate”). The English word is cognate with Middle High German knochen(“to hit”), Old English cnuian, cnuwian(“to pound, knock”), Old Norse knoka (compare Danish knuge, Swedish knocka(“to hug”)).

etymonline

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knock (v.)

Old English cnocian (West Saxon cnucian), "to pound, beat; knock (on a door)," likely of imitative origin. Figurative meaning "deprecate, put down" is from 1892. Related: Knocked; knocking. Of engines from 1869. To knock back (a drink) "swallow quickly or at a gulp" is from 1931. Many phrases are in reference to the auctioneer's hammer, for example knock down (v.) "dispose of (something) at auction" (1760).

knock (n.)

mid-14c., from knock (v.). As an engine noise, from 1899.