incredulity vs doubtfulness

incredulity and doubtfulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
incredulity	Yes	No	No	No
doubtfulness	Yes	No	No	No

As nouns, doubtfulness is a hypernym of incredulity; that is, doubtfulness is a word with a broader meaning than incredulity:

Other hypernyms of incredulity include doubt, dubiety, dubiousness, incertitude, uncertainty.

incredulity (noun)	doubtfulness (noun)
doubt about the truth of something	uncertainty about the truth or factuality or existence of something
	the state of being unsure of something