facer vs difficultness

facer and difficultness both are nouns.

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

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

facer: (a dated Briticism) a serious difficulty with which one is suddenly faced
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 facer include difficulty.

facer (noun)	difficultness (noun)
(a dated Briticism) a serious difficulty with which one is suddenly faced	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result