means Water heated past boiling into an invisible gas, whose expansive force has been harnessed to drive engines, cook food, and clean things.

from From Old English 'stēam,' meaning vapor or rising mist, with cousins across the Germanic languages — Dutch 'stoom,' for instance. The word long predates the engines it would later power; for centuries it simply named the breath of hot water and the haze off a pot. Only with the industrial age did 'steam' come to mean might itself, lending us phrases like 'full steam ahead' and 'letting off steam.'