Enter a clue or pattern or both:
The Clue
River basin (9 letter answer)
The Answer
WATERSHED
Tags
Notes
The answer WATERSHED is so rare that it appears less than once every 2500 puzzles.
Definition
WATERSHED as a noun:
1. (watershed, water parting, divide) = a ridge of land that separates two adjacent river systems
2. (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"