Open English Wordnet
Nouns
(n)river basin, basin, watershed, drainage basin, catchment area, catchment basin, drainage areathe 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”
(n)landmark, turning point, watershedan 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”