difficultness vs difficult

difficultness is a noun but difficult is not a noun.

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

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

difficultness (adjective)	difficult (adjective)
	not easy; requiring great physical or mental effort to accomplish or comprehend or endure
	hard to control