one million million million vs Britain

one million million million and Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
one million million million	Yes	No	No	No
Britain	Yes	No	No	No

one million million million (noun)	Britain (noun)
the number that is represented as a one followed by 18 zeros in the UK	a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom