Coup

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late 18th century: from French, from medieval Latin colpus ‘blow’ (see cope1).

wiktionary

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Borrowed from French coup(“blow, strike”), from Late Latin colpus, from Latin colaphus. Doublet of colpus.

etymonline

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coup (n.)

c. 1400, "a blow" (obsolete), from Old French coup, colp "a blow, strike" (12c.), from Medieval Latin colpus, from Vulgar Latin *colapus, from Latin colaphus "a cuff, box on the ear," from Greek kolaphos "a blow, buffet, punch, slap," "a lowly word without clear etymology" [Beekes].

Meaning "a sudden decisive act" is 1852, short for coup d'etat. In Modern French the word is a workhorse, describing everything from a pat on the back to a whipping, and is used as well of thunder, gusts of wind, gunshots, and chess moves.