The whole region or extent of country which contributes to the supply of a river or lake.
- A ridge of high land dividing two areas that are drained by different river systems. Also called water parting.
- The region draining into a river, river system, or other body of water.
- A critical point that marks a division or a change of course; a turning point: "a watershed in modern American history, a time that ... forever changed American social attitudes” ( Robert Reinhold).