Christianity vs Christian

Christianity and Christian both are nouns.

Word	Noun	Adjective	Verb	Adverb
Christianity	Yes	No	No	No
Christian	Yes	Yes	No	No

Christianity (noun)	Christian (noun)
a monotheistic system of beliefs and practices based on the Old Testament and the teachings of Jesus as embodied in the New Testament and emphasizing the role of Jesus as savior	a religious person who believes Jesus is the Christ and who is a member of a Christian denomination
the collective body of Christians throughout the world and history (found predominantly in Europe and the Americas and Australia)

Christianity (adjective)	Christian (adjective)
	relating to or characteristic of Christianity