Water wheel \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.

Source: Webster's Revised Unabridged Dictionary (1913)