WATERSHED

Definition

1. noun a ridge of land that separates two adjacent river systems. — synonyms: water_parting, divide
2. noun the entire geographical area drained by a river and its tributaries. — synonyms: river_basin, basin, drainage_basin, catchment_area, catchment_basin, drainage_area
3. noun an event marking a unique or important historical change of course or one on which important developments depend. — synonyms: landmark, turning_point