deterrent vs difficultness

deterrent and difficultness both are nouns.

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

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

deterrent: something immaterial that interferes with or delays action or progress
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 deterrent include difficulty.

deterrent (noun)	difficultness (noun)
something immaterial that interferes with or delays action or progress	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result

deterrent (adjective)	difficultness (adjective)
tending to deter