This is my first post also . . .
anth82: My first thought was if there were any chance that you accidentally DELETED this dictionary from your device?? If so, then it should show up in the "archives", right?
But . . . as Tiersten pointed out, the two dictionaries that came with my Kindle 3
cannot be deleted from the device?
One of the reasons I wanted to get an e-reader was the ability to quickly look up words as I read! As a new user, all I know at this point is that you can set one dictionary or the other as the main one. I am using the "New Oxford American" as the default that my device shipped with. I have looked at the other one, the "Oxford Dictionary of English", but, so far, do not see any real difference between them. One thing at a time.
Perhaps you could try a "Reset" (or a "Hard Reset") of your device If either of those didn't work, I would contact Amazon Customer Service.
All best, and still way early into the Kindle learning curve,
Joe