river vs Mekong

river and Mekong both are nouns.

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

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