Rostov on Don vs Rostov-on-Don

Rostov on Don and Rostov-on-Don both are nouns.

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

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

Rostov on Don 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 on Don include Rostov, Rostov na Donu.

Rostov on Don (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