City of London vs Greater London

City of London and Greater London both are nouns.

Word	Noun	Adjective	Verb	Adverb
City of London	Yes	No	No	No
Greater London	Yes	No	No	No

City of London (noun)	Greater London (noun)
the part of London situated within the ancient boundaries; the commercial and financial center of London	the capital and largest city of England; located on the Thames in southeastern England; financial and industrial and cultural center