retention basin vs watershed

retention basin and watershed both are nouns.

Word	Noun	Adjective	Verb	Adverb
retention basin	Yes	No	No	No
watershed	Yes	No	No	No

As nouns, watershed is a hypernym of retention basin; that is, watershed is a word with a broader meaning than retention basin:

retention basin: a storage site similar to a detention basin but the water in storage is permanently obstructed from flowing downstream
watershed: the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet

Other hypernyms of retention basin include basin, catchment area, catchment basin, drainage area, drainage basin, river basin.

retention basin (noun)	watershed (noun)
a storage site similar to a detention basin but the water in storage is permanently obstructed from flowing downstream	an event marking a unique or important historical change of course or one on which important developments depend
	a ridge of land that separates two adjacent river systems
	the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet