Eternal City vs Italian capital

Eternal City and Italian capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
Eternal City	Yes	No	No	No
Italian capital	Yes	No	No	No

As nouns, Eternal City and Italian capital are synonyms defined as:

Eternal City and Italian capital: capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire

Other synonyms of Eternal City include capital of Italy, Roma, Rome.

Eternal City (noun)	Italian capital (noun)
capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire	capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire