A variant of 'pound' (enclosure) — a pond was an enclosed, penned-up body of water.
A small body of still water formed naturally or by artificial means.
An unexplained variant of 'pound' (an enclosure), from Old English 'pund' meaning 'enclosure.' A pond was originally an enclosed body of water — a 'pounded' or penned-up pool. Key roots: pund (Old English: "enclosure").