river basin vs drainage basin

river basin and drainage basin both are nouns.

Word	Noun	Adjective	Verb	Adverb
river basin	Yes	No	No	No
drainage basin	Yes	No	No	No

As nouns, river basin and drainage basin are synonyms defined as:

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

Other synonyms of river basin include basin, catchment area, catchment basin, drainage area, watershed.

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