Red China vs Cathay

Red China and Cathay both are nouns.

Word	Noun	Adjective	Verb	Adverb
Red China	Yes	No	No	No
Cathay	Yes	No	No	No

As nouns, Red China and Cathay are synonyms defined as:

Red China and Cathay: a communist nation that covers a vast territory in eastern Asia; the most populous country in the world

Other synonyms of Red China include China, Communist China, mainland China, People's Republic of China, PRC.

Red China (noun)	Cathay (noun)
a communist nation that covers a vast territory in eastern Asia; the most populous country in the world	a communist nation that covers a vast territory in eastern Asia; the most populous country in the world