1. (

• watershed ,
• water_parting ,
• divide

) a ridge of land that separates two adjacent river systems ;

2. (

• river_basin ,
• basin ,
• watershed ,
• 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" ;

3. (

• landmark ,
• turning_point ,
• watershed

) 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" ;