furnace (n.) Look up furnace at Dictionary.com
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- "warm" (cognates: Greek thermos, Old English wearm; see warm (adj.)).