Meaning

noun a ridge of land that separates two adjacent river systems

noun the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet

noun an event marking a unique or important historical change of course or one on which important developments depend

originFrom water + shed. A calque of German Wasserscheide.

Etymology from Wiktionary, CC BY-SA 3.0