problem vs difficultness

problem and difficultness both are nouns.

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

As nouns, difficultness is a hypernym of problem; that is, difficultness is a word with a broader meaning than problem:

problem: a source of difficulty
difficultness: 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 problem include difficulty.

As nouns, difficultness is a hypernym of problem; that is, difficultness is a word with a broader meaning than problem:

problem: a state of difficulty that needs to be resolved
difficultness: 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 problem include difficulty.

problem (noun)	difficultness (noun)
a source of difficulty	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result
a question raised for consideration or solution
a state of difficulty that needs to be resolved