Wa·ter wheel
  1. Any wheel for propelling machinery or for other purposes, that is made to rotate by the direct action of water; -- called an overshot wheel when the water is applied at the top, an undershot wheel when at the bottom, a breast wheel when at an intermediate point; other forms are called reaction wheel, vortex wheel, turbine wheel, etc.
  2. The paddle wheel of a steam vessel.
  3. A wheel for raising water; a noria, or the like.
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  water wheel
       n 1: a wheel with buckets attached to its rim; raises water from
            a stream or pond [syn: waterwheel]
       2: a wheel that rotates by direct action of water; a simple
          turbine [syn: waterwheel]