double Dutch vs Great Britain

double Dutch and Great Britain both are nouns.

Word	Noun	Adjective	Verb	Adverb
double Dutch	Yes	No	No	No
Great Britain	Yes	No	No	No

double Dutch (noun)	Great Britain (noun)
the difficult version of jump rope in which players jump over two ropes that are swung in a crisscross manner by two turners	an island comprising England and Scotland and Wales
an incomprehensible talk	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