furnace (n.) Look up furnace at Dictionary.com
early 13c., from Old French fornaise "oven, furnace" (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.)).