Cathay vs Red China

Cathay and Red China both are nouns.

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

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

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

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

Cathay (noun)	Red China (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