watershed

Noun

• 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
    

• 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
    

• a ridge of land that separates two adjacent river systems

Related words

• Synonyms: 
  landmark , turning point , river basin , basin , drainage basin , catchment area , catchment basin , drainage area , water parting , divide