whats the longest word you can think of?

[Pant Leg Eater from the Bad World]

Antidisestablishmentarianism...

EDIT:

Pneumoultramicroscopicsilicovolcaniconeo sis. That's definitely spelled wrong, but I memorized how to say that word a while ago (I didn't cheat, I swear). It's some kind of lung disease caused by inhaling volcano ash.

I thought that had been proven to be a hoax word... Eh. Maybe not. I dunno.