stagnum

Noun

 * 1)  A millpond.
 * 2) * 1865, John Fisher (of Masham.), The History and Antiquities of Masham and Mashamshire (page 182)
 * See ante p. 44, where allusion is made to the grant by Roger de Mowbray to John, son of Drin, who had liberty to make this mill, and to fasten a stagnum or mill-pool.

Etymology 1
Possibly from, source of Ancient Greek , with different ablaut grade. Conversely, possibly related to Ancient Greek.

Noun

 * 1) pond, swamp, fen; any piece of standing water
 * 2)  waters
 * 3)  any pool or lake in general

Usage notes
The use of the spelling stagnum as a form of is unattested before Pliny. Some analyses suspect a Gaulish interference may have caused the rise of this alternative form.