Penultimate
Have you ever used the word "penultimate" in a sentace? I haven't, but I've heard people use it, and I thought I knew what it meant. I know that I thought it meant what they thought it meant... Aparently (and I've verified this both @ dictionary.com and with my father) I was wrong.
Also, antepenultimate means... no, not the opposite of penultimate (that would be antipenultimate I would immagine), it means the third from the last. What the hell? Where was I when someone came up with the "ante" prefix? Penultimate = next to the last. Antepenultimate = coming before the next to the last. What kind of world are we living in when I didn't realize that there was a whole prefix I wasn't using?!?
And to answer your unasked question: No. I haven't been sleeping enough.
-Jon