difficultness vs difficulty

difficultness and difficulty both are nouns.

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

As nouns, difficultness and difficulty are synonyms defined as:

difficultness and difficulty: the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result

difficultness (noun)	difficulty (noun)
the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result	an effort that is inconvenient
	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result