D defs.my
Entry 3 senses Webster, 1913

Watershed

/wôʹtərshĕd/ · Wa·ter·shed · IPA /ˈwɔtɚʃɛd/
01 n. The whole region or extent of country which contributes to the supply of a river or lake.
  1. 1.
    The whole region or extent of country which contributes to the supply of a river or lake.
  2. 2.
    The line of division between two adjacent rivers or lakes with respect to the flow of water by natural channels into them; the natural boundary of a basin; -- called also divide and water parting. Also: divide, water parting
  3. 3.
    a point in time marking an important transition between two situations, or phases of an activity; a turning point.