Po River vs Po

Po River and Po both are nouns.

Word	Noun	Adjective	Verb	Adverb
Po River	Yes	No	No	No
Po	Yes	No	No	No

As nouns, Po River and Po are synonyms defined as:

Po River (noun)	Po (noun)
a European river; flows into the Adriatic Sea	a European river; flows into the Adriatic Sea
	a radioactive metallic element that is similar to tellurium and bismuth; occurs in uranium ores but can be produced by bombarding bismuth with neutrons in a nuclear reactor