Westminster vs City of Westminster

Westminster and City of Westminster both are nouns.

Word	Noun	Adjective	Verb	Adverb
Westminster	Yes	No	No	No
City of Westminster	Yes	No	No	No

As nouns, Westminster and City of Westminster are synonyms defined as:

Westminster and City of Westminster: a borough of Greater London on the Thames; contains Buckingham Palace and the Houses of Parliament and Westminster Abbey

Westminster (noun)	City of Westminster (noun)
a borough of Greater London on the Thames; contains Buckingham Palace and the Houses of Parliament and Westminster Abbey	a borough of Greater London on the Thames; contains Buckingham Palace and the Houses of Parliament and Westminster Abbey