oppressiveness vs difficulty

oppressiveness and difficulty both are nouns.

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

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

oppressiveness: unwelcome burdensome difficulty
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 oppressiveness include difficultness.

oppressiveness (noun)	difficulty (noun)
unwelcome burdensome difficulty	an effort that is inconvenient
a feeling of being oppressed	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result