niceness vs difficulty

niceness and difficulty both are nouns.

Word	Noun	Adjective	Verb	Adverb
niceness	Yes	No	No	No
difficulty	Yes	No	No	No

As nouns, difficulty is a hypernym of niceness; that is, difficulty is a word with a broader meaning than niceness:

niceness: the quality of being difficult to detect or analyze
difficulty: the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result

Other hypernyms of niceness include difficultness.

niceness (noun)	difficulty (noun)
the quality of nice	an effort that is inconvenient
the quality of being difficult to detect or analyze	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result
a courteous manner that respects accepted social usage