scepticism vs doubtfulness

scepticism and doubtfulness both are nouns.

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

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

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

scepticism (noun)	doubtfulness (noun)
the disbelief in any claims of ultimate knowledge	uncertainty about the truth or factuality or existence of something
doubt about the truth of something	the state of being unsure of something