millpond

mill +‎ pond

millpond (plural millponds)

1. A pond or reservoir produced by damming a river or stream in order to provide a steady source of water for a millrace.
   • 1886, Peter Christen Asbjørnsen, translated by H.L. Brækstad, Folk and Fairy Tales, page 152:

     When I came to the saw-mill at Brække, the sky was overcast, it was already growing dark, only above the level of the north-western horizon there appeared a streak of light, which threw a subdued glimmer on the tranquil surface of the mill-pond.

• calm as a millpond

• milldam, millrace