[fur-nis] 
noun, verb, -naced, -nac⋅ing.| 1. | a structure or apparatus in which heat may be generated, as for heating houses, smelting ores, or producing steam. |
| 2. | a place characterized by intense heat: The volcano was a seething furnace. |
| 3. | (initial capital letter ) Astronomy. the constellation Fornax. |
| 4. | to heat (a metal piece) in a furnace. |