A watershed is a turning point, or historic moment. The day you got your braces off might have been a watershed moment in your life.

Watershed is a geographical term, originally. The area that drains into a single river is the watershed for that river. Watershed can also mean a ridge, like that formed by a chain of mountains, which sends water to two different rivers on either side. It's from this meaning that watershed came to mean a turning point or dividing line in social life.

Definitions of watershed

n a ridge of land that separates two adjacent river systems

divide, water parting
Great Divide
that part of the continental divide formed by the Rocky Mountains in the United States
continental divide
the watershed of a continent (especially the watershed of North America formed by a series of mountain ridges extending from Alaska to Mexico)
Type of:
a spatial location defined by a real or imaginary unidimensional extent

n the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet

basin, catchment area, catchment basin, drainage area, drainage basin, river basin
detention basin
a storage site (such as a small reservoir) that delays the flow of water downstream
retention basin
a storage site similar to a detention basin but the water in storage is permanently obstructed from flowing downstream
Type of:
geographic area, geographic region, geographical area, geographical region
a demarcated area of the Earth

n an event marking a unique or important historical change of course or one on which important developments depend

“the agreement was a watershed in the history of both nations”
landmark, turning point
Fall of Man
(Judeo-Christian mythology) when Adam and Eve ate of the fruit of the tree of knowledge of good and evil in the Garden of Eden, God punished them by driving them out of the Garden of Eden and into the world where they would be subject to sickness and pain and eventual death
road to Damascus
a sudden turning point in a person's life (similar to the sudden conversion of the Apostle Paul on the road from Jerusalem to Damascus of arrest Christians)
Type of:
juncture, occasion
an event that occurs at a critical time

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