Furnace

google

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Middle English: from Old French fornais(e ), from Latin fornax, fornac-, from fornus ‘oven’.

wiktionary

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From Middle English forneys, from Old French fornais (French fournaise), from Latin fornāx.

etymonline

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furnace (n.)

early 13c., from Old French fornais "oven, furnace," figuratively "flame of love" (12c.), from Latin fornacem (nominative fornax) "an oven, kiln," related to fornus/furnus "oven," and to formus "warm," from PIE root *gwher- "to heat, warm."