unskillfulness vs inability

unskillfulness and inability both are nouns.

Word	Noun	Adjective	Verb	Adverb
unskillfulness	Yes	No	No	No
inability	Yes	No	No	No

As nouns, inability is a hypernym of unskillfulness; that is, inability is a word with a broader meaning than unskillfulness:

unskillfulness (noun)	inability (noun)
a lack of cognitive skill	lacking the power to perform
	lack of ability (especially mental ability) to do something