Oslo vs Christiania

Oslo and Christiania both are nouns.

Word	Noun	Adjective	Verb	Adverb
Oslo	Yes	No	No	No
Christiania	Yes	No	No	No

As nouns, Oslo and Christiania are synonyms defined as:

Oslo and Christiania: the capital and largest city of Norway; the country's main port; located at the head of a fjord on Norway's southern coast

Other synonyms of Oslo include capital of Norway.

Oslo (noun)	Christiania (noun)
the capital and largest city of Norway; the country's main port; located at the head of a fjord on Norway's southern coast	the capital and largest city of Norway; the country's main port; located at the head of a fjord on Norway's southern coast