Well Googled! ;) That's the official answer I think, but the weirdo in me (ie me) can't see why it can't just be "E". I guess that's what you're supposed to guess, 'wrongly', but why is it wrong? I think if you specify word, which I didn't, hmm...
Anyway, I did just do a search and apparently this is complicated/controversial matter. Possibilities:
1. Envelope
2. E
3. Eye
4. Maybe more
(3) supposedly because it sounds like I or has just one letter between the Es.
Maybe the UN can sort this out, if they're not busy right now.
I only really used it as a distraction for 2, which is annoying to be the 'victim of' but fun to inflict on other people.
