#1 watershed n. [water parting, divide] a ridge of land that separates two adjacent river systems. wn
#2 watershed n. [river basin, basin, drainage basin, catchment area, catchment basin, drainage area] the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet; "flood control in the Missouri basin". wn
#3 watershed n. [landmark, turning point] 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". wn
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