Look up some crazy sounding 20+ character word, takes three steps, and then you get a definition of the sub-sub-sub word and it says ".... blah blah, derived from the Greek base <abc>- and then also the Latin base -<xyz>", and you realize you had no chance at getting it from any kind of first principles or anything.
For what it's worth, the first two steps in your lookup would come naturally to a native speaker- it's a suffix formation similar to e.g. "cleanliness" and "friendliness".
"Curmudgeon" itself is interesting, because while it's not particularly common, I actually think a lot of native English speakers would recognize it because it's got a lot of character- for some reason, the way it feels to say and the way it sounds almost has some of the character of the meaning.
Look up some crazy sounding 20+ character word, takes three steps, and then you get a definition of the sub-sub-sub word and it says ".... blah blah, derived from the Greek base <abc>- and then also the Latin base -<xyz>", and you realize you had no chance at getting it from any kind of first principles or anything.