1) an enclosed apparatus with a fire, used for heating metals, making glass etc in a factory (furnace)

2) an apparatus for supplying warmth to a room or for heating water etc (heater)

3) (of milk, cream) with bacteria that produce disease killed by heating (pasteurized)

4) of stave; a closed apparatus burning wood, coal, gas, oil etc, used for cooking, heating etc (stove)

5) a (mentioned) state or condition of the mind; to harden (metal) by heating and cooling; to make (a judgement etc) less severe (temper)