n.1 a fuel-burning apparatus for heating a hot-water supply.
2 a tank for heating water, esp. for turning it to steam under pressure.
3 a metal tub for boiling laundry etc.
4 a fowl, vegetable, etc., suitable for cooking only by boiling.
Phrases and idioms:
boiler-room a room with a boiler and other heating equipment, esp. in the basement of a large building. boiler suit a one-piece suit worn as overalls for heavy manual work.