Once when I was in school, my right eyelid went all weird for several days: it was itchy and puffy, and kind of sore. So finally, I decided there might be something wrong and went to health services. The nurse there examined my eye for a little while and said, "looks like you have blepharitis."

Freaky-sounding, huh? I was scared. Turns out it means "swollen eyelid" I didn't get any medication or advice out of them (it eventually went away on its own) but I did learn a new word, and an impressive one at that!