Peterburg vs Petrograd

Peterburg and Petrograd both are nouns.

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

As nouns, Peterburg and Petrograd are synonyms defined as:

Peterburg and Petrograd: 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 Peterburg include Leningrad, Saint Petersburg, St. Petersburg.

Peterburg (noun)	Petrograd (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