The Oxford English Dictionary.It calls itself "the definitive record of the English Language," and rightly so. If you're a writer, a poet, or just a "word-lover" (first documented usage in 1857, says the OED), you might lose yourself in it for awhile. Possibly to the annoyance of those around you who don't quite share your enthusiasm. (Ahem.)For those unfamiliar with the OED, here is its claim to fame:
"As a historical dictionary, the OED is very different from those of current English, in which the focus is on present-day meanings. You'll still find these in the OED, but you'll also find the history of individual words, and of the language — traced through 3 million quotations, from classic literature and specialist periodicals to film scripts and cookery books."