Petrograd vs Peterburg

Petrograd and Peterburg both are nouns.

Word	Noun	Adjective	Verb	Adverb
Petrograd	Yes	No	No	No
Peterburg	Yes	No	No	No

As nouns, Petrograd and Peterburg are synonyms defined as:

Petrograd and Peterburg: a city in the European part of Russia; 2nd largest Russian city; located at the head of the Gulf of Finland; former capital of Russia

Other synonyms of Petrograd include Leningrad, Saint Petersburg, St. Petersburg.

Petrograd (noun)	Peterburg (noun)
a city in the European part of Russia; 2nd largest Russian city; located at the head of the Gulf of Finland; former capital of Russia	a city in the European part of Russia; 2nd largest Russian city; located at the head of the Gulf of Finland; former capital of Russia