ruggedness vs difficulty

ruggedness and difficulty both are nouns.

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

As nouns, difficulty is a hypernym of ruggedness; that is, difficulty is a word with a broader meaning than ruggedness:

ruggedness: the quality of being difficult to do
difficulty: 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 ruggedness include difficultness.

ruggedness (noun)	difficulty (noun)
the property of being big and strong	an effort that is inconvenient
the quality of being topologically uneven	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result
the quality of being difficult to do