detention basin vs watershed

detention basin and watershed both are nouns.

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

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

detention basin: a storage site (such as a small reservoir) that delays the flow of water 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 detention basin include basin, catchment area, catchment basin, drainage area, drainage basin, river basin.

detention basin (noun)	watershed (noun)
a storage site (such as a small reservoir) that delays the flow of water 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