The term 'SOURCE OF STEAM' can be broken down into two crossword solutions: IRON (4 letters) and BOILER (6 letters). An IRON is a device that uses steam to press clothes and other fabrics. It is heated by electricity or gas, and the steam is generated by boiling water in a BOILER. A BOILER is a closed vessel in which water or other fluid is heated. Boilers are used to generate steam for a variety of purposes, such as powering turbines, heating buildings, and providing hot water.