mainland China vs China

mainland China and China both are nouns.

Word	Noun	Adjective	Verb	Adverb
mainland China	Yes	No	No	No
China	Yes	No	No	No

As nouns, mainland China and China are synonyms defined as:

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

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

mainland China (noun)	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
	a government on the island of Taiwan established in 1949 by Chiang Kai-shek after the conquest of mainland China by the Communists led by Mao Zedong