unbelief vs skepticism

unbelief and skepticism both are nouns.

Word	Noun	Adjective	Verb	Adverb
unbelief	Yes	No	No	No
skepticism	Yes	No	No	No

As nouns, skepticism is a hyponym of unbelief; that is, skepticism is a word with a more specific, narrower meaning than unbelief:

Other hyponyms of unbelief include agnosticism, scepticism, atheism.

unbelief (noun)	skepticism (noun)
a rejection of belief	doubt about the truth of something
	the disbelief in any claims of ultimate knowledge