The term 'water boiler' can be summarized as a KETTLE, which is a 6-letter word. A KETTLE is a type of pot used for boiling water, usually made of metal or other heat-resistant material. It is often used to make tea or other hot beverages. Kettles are also used for cooking, such as for making soups and stews. Kettles come in a variety of sizes and shapes, and can be powered by electricity, gas, or even wood.