Mekong vs river

Mekong and river both are nouns.

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

Mekong (noun)	river (noun)
an Asian river; flows through a large delta in southern Vietnam into the South China Sea	a large natural stream of water (larger than a creek)