Brunt

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late Middle English (denoting a blow or an attack, also the force or shock of something): of unknown origin.

wiktionary

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From Middle English brunt, bront, from Old Norse brundr or brundtíð(“ oestrus, rut”), or bruna(“to rush”).

etymonline

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brunt (n.)

late 14c., "a sharp blow," of uncertain origin, perhaps from Old Norse brundr "sexual heat," or bruna "to advance like wildfire" (said of a ship under sail, etc.). Meaning "chief force, the heaviest or worst (of something)," as in bear the brunt, is from early 15c.