The term 'water heater' can be described by two crossword solutions: KETTLE and BOILER. A KETTLE is a small container with a spout, handle, and lid used for boiling water. A BOILER is a large vessel that heats water to produce steam or hot water for heating or power. Both kettles and boilers are used to heat water, but the size and purpose of each device differs. Kettles are typically used to heat water for drinking or cooking, while boilers are used to provide hot water or steam for industrial or residential heating systems.