Knock
Old English cnocian, of imitative origin.
wiktionary
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
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.
