We now have the Historical Thesaurus of the Oxford English Dictionary with Additional Material from "A Thesaurus of Old English" in our reference collection. The call number for this source is King Reference PE1591 .H55 2009. It was 45 years in the making, and some are calling it the last great reference book.
The thesaurus is two volumes and contains over 800,000 meanings. The first volume is the thesaurus itself. It’s arranged semantically instead of alphabetically. The three major categories are the external world, the mental world, and the social world. Each of those categories are then further subdivided into categories. For instance the mental world includes categories like mental capacity, emotion, philosophy, etc. Each individual entry then lists words with similar meanings in chronological order. The second volume is the index for the work, which is an alphabetic list that helps you locate specific words in the first volume. If you're interested in finding out more about how it works, this article might be helpful. It includes a short video that walks you through it.
Just as the Oxford English Dictionary is more complex than a regular dictionary, the Historical Thesaurus is more complex than a regular thesaurus. It's meant to be a historical analysis of how meanings of words have changed over time. You can find out when a specific word began to mean one thing, and when another word began to have the same meaning. In addition to being a useful tool for academic research, it's a tool that could be used by a writer of historical fiction who wants to make sure his or her dialogue is realistic. Also, it can be fun to look up slang terms and insults. For instance the next time you have a friend do something rude, you can tell them they are being unbene (1375), ingenteel (1658-1787), or blowzy (1851)!