The harder words are trivia questions an educated English native could get. What I mean by this is they're all words that you'd have a chance of knowing for a reason. Things like defenestrate, antidisestablishmentarianism, hippopotomonstrosesquipedaliophobia. I know these words, but these are not words I know because I've ever had cause to use them. Words can get way harder than this and still be actually used, and not strictly only in a scientific sense. I'm thinking things like "Ginnel" (narrow passage between houses) or "Vamp" (a part of a shoe) or "Moraines" (hilly landscape formed by glaciers) or "Lea" (land used to pasture animals)