The Oxford University Press is continuing to push the envelope on reference books, with the Historical Thesaurus of the Oxford English Dictionary. It's a 3952-page behemoth that not only includes every word in the OED, but traces meanings through history as well. It took 44 years to write, and weighs 14½ pounds.
It looks like pure lexicographical porn. There are some detractors, though, specifically about the classification scheme. The Amazon page has an annotated sample page, which shows that "express ill-humor" is categorized as "02.02.21.05.04.01", hardly a friendly scheme. I'm used to the Roget system, which is also numerical, but doesn't hew so slavishly to a strict hierarchy, so those same concepts can be found at 951.15, a number better fitted to my short-term memory capacity. I can imagine flipping back and forth quite a bit between index and content: "02.02.21.what?"
But this still looks to be a very impressive achievement, the first and maybe last of its kind. I'll have to find a physical copy some place to further examine (peruse, study, inspect, scrutinize, check up on).