The folks at Oxford University Press have finally finished their Historical Thesaurus of The Oxford English Dictionary after more than 40 years of effort. The book contains 4448 pages and nearly every word in the English language (according to the OED). I like that the synonyms are listed chronologically but this thing is crying out to be put online (or in some electronic format)...what a boon it would be for period novelists to able to press the "write like they did in 1856" button. Available for pre-order at Amazon for $316. (via long now)
Update: There will be an online version of the thesaurus...at some point.