hookey (alternatively 'hooky'), noun -- apparently originating from a slang phrase hook it -- to make off. It first appeared in 1848. This is roughly when public schools began to be widespread in America. Not a coincidence, I'm sure. To be a hookey is to be a truant. We all know it in the phrase to play hookey.
One could consider this a synomym for AWOL, I suppose.
While we're on the topic of words, here's one I'd never heard before:
retreatant -- a person on a religious retreat. Some friends of mine are organizing a retreat, and used this word in their flyer. I was ready to pounce on them in school-marmish disapproval, but ...