A waterwheel is a big wheel with flat boards or buckets around its edge. Running water pushes against them, the wheel turns, and that turning drives a machine — most famously the heavy stones inside a mill that grind wheat into flour. This is one of the oldest machines people have: water does the work that a person or an animal would otherwise have to do. There is a second kind, working the other way round: a wheel turned by an animal or by people, which lifts water up out of a river into the fields. Farmers in many countries used these for irrigation. Both are called waterwheels, and both ideas are worth holding, because the word is really about the meeting of wheel and water, in either direction. Today you will meet the word mostly in history lessons, in tourist places (old mills kept working for visitors), and in stories set long ago. Because of that, it carries a warm, old-fashioned feeling — turning slowly, dripping, a little green with moss. If you want the modern machine that makes electricity from a river, that is a turbine, not a waterwheel. People sometimes write it as two words, water wheel; both spellings are fine, and dictionaries differ.

水車（水力驅動的大輪，用來推動磨坊等機械）