The Phrontistery: a compendium of lost words. Here are the rules for determining if a word is lost:

1. The word must have a header entry in the Oxford English Dictionary.
2. The word may not appear in its proper English context on any readily accessible web page.
3. The word must have been used in Modern English.
4. The word must have been used in a standard English variety rather than simply in a regional dialect.
5. The word must not be a simple variation in spelling of another word.

There's a ton of good stuff here, but the best lost word I saw on my first look-through was dicaearchy.

dicaearchy n 1656 -1658
just government
While we dream of living in a dicaearchy, in truth, we're governed by dicks.

Via Cynical-C.