Excellent episode. That's the episode where embiggens was born.
ETA: I should say I meant born on the Simpsons. It was intended to be a made up word, however it was later discovered that it had been used once in the late 1800s. And now you have fulfilled your learn something new for the day.
ETA2: The word cromulent was also first used in that episode. It's completely made up and while it's not in the paper version of the dictionary, it does appear in Webster's online version.