Great Britain vs double Dutch

Great Britain and double Dutch both are nouns.

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

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