That's a pretty lame rule if I may say so myself. Kinda of violates the whole spirit of the game. You have to use real words that you know how to spell. Requiring a definition, especially one that matches some chosen dictionary, opens up a lot of weird challenge problems. Definitions are much more fluid than spelling (although spellings can change over time as well). Spelling and whether or not a word is "real" tend to be much more cut and dry.