Rostov vs Rostov-on-Don

Rostov and Rostov-on-Don both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rostov	Yes	No	No	No
Rostov-on-Don	Yes	No	No	No

As nouns, Rostov and Rostov-on-Don are synonyms defined as:

Rostov and Rostov-on-Don: a seaport on the Don River near the Sea of Azov in the European part of Russia

Other synonyms of Rostov include Rostov na Donu, Rostov on Don.

Rostov (noun)	Rostov-on-Don (noun)
a seaport on the Don River near the Sea of Azov in the European part of Russia	a seaport on the Don River near the Sea of Azov in the European part of Russia