watershed

noun ! Definition from WordNet 3.1, Princeton University. Pronunciation from Wiktionary, via Kaikki.org. More about watershed at Wordnik → Where our words come from →

1. A ridge of land that separates two adjacent river systems.
2. 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. 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