Tigris River vs Tigris

Tigris River and Tigris both are nouns.

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

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

Tigris River and Tigris: an Asian river; a tributary of the Euphrates River

Tigris River (noun)	Tigris (noun)
an Asian river; a tributary of the Euphrates River	an Asian river; a tributary of the Euphrates River