watercourse vs river

watercourse and river both are nouns.

Word	Noun	Adjective	Verb	Adverb
watercourse	Yes	No	No	No
river	Yes	No	No	No

As nouns, river is a hyponym of watercourse; that is, river is a word with a more specific, narrower meaning than watercourse:

watercourse (noun)	river (noun)
a conduit through which water flows	a large natural stream of water (larger than a creek)
a natural body of running water flowing on or under the earth
natural or artificial channel through which water flows