The Historical Thesaurus of the Oxford English Dictionary

For a very long time, I have actively desired a book that would tell me what a word meant in a given time period, rather than if it was simply used. Words over time change their meaning.Various etymology sites helped but many times I was left floundering.
 And for years, I have silently gritted my teeth with the whole reticule/ridicule debate. Which came first? For me it seemed an impossibility that reticule was derived from ridicule.
Then the Historical Thesaurus of the Oxford English Dictionary was published last year and I took possession of my copy just before the RWA conference. It is the definitive resource for such a thing.
In the question of women's bags: 1801-1806 they  were indispensables, 1801- present day reticule and 1805-1838 ridicule.  Handbag starts in 1923. Forgive me but I punched the air. 
It makes things so much easier to check on if a word had that given meaning during that period. For example, I checked hot-foot as he hot-footed up somewhere. Nope. Not in use with that meaning during 1848. I used ran like a redshank instead as it was in use.

It is also interesting to see when certain things start being named. It is sure to become an indispensable part of my revisions. It helps to give a more authentic feel to the work.
The entire book was 45 years in production and it is expensive.  There are two large volumes and a complicated reference system. I would imagine that most university libraries have it, but it is much handier just to be able to look up a word.
My very lovely husband said when I asked for it for Christmas that if I needed it for my work, I should just get it.  Luckily I did as the Folio Society had it on special offer and they are no longer stocking it. You can still get it through Amazon.
Apparently there are plans to put the whole thing on disc and cross reference with the OED. However, I like paper. You discover things as you flip through, staring at the mouse-print.
If you lust after words and their meanings, or if you write historical novels, this is fantastic resource.