Danau vs Danube River

Danau and Danube River both are nouns.

Word	Noun	Adjective	Verb	Adverb
Danau	Yes	No	No	No
Danube River	Yes	No	No	No

As nouns, Danau and Danube River are synonyms defined as:

Danau and Danube River: the 2nd longest European river (after the Volga); flows from southwestern Germany to the Black Sea

Other synonyms of Danau include Danube.

Danau (noun)	Danube River (noun)
the 2nd longest European river (after the Volga); flows from southwestern Germany to the Black Sea	the 2nd longest European river (after the Volga); flows from southwestern Germany to the Black Sea