【Unbelief】 , 【disbelief】 , 【incredulity】 are comparable when they mean the attitude or state of mind of one who does not believe.
【Unbelief】 stresses the lack or absence of belief especially in respect to something (as religious revelation) above and beyond one′s personal experience or capacity.
【Disbelief】 implies a positive rejection of what is stated or asserted.
【Incredulity】 implies indisposition to believe or, more often, a skeptical frame of mind.