Oxford English Dictionary

The Oxford English Dictionary is the world's leading authority on the development of the English language over the last millennium.  It is an unsurpassed guide to the meaning, history and pronunciation of over half a million words through 2.5 million quotations from a wide range of international sources.

"The OED covers words from across the English-speaking world, from North America to South Africa, from Australia and New Zealand to the Caribbean.  It also offers the best in etymological analysis and in listing of variant spellings, and it shows pronunciation using the International Phonetic Alphabet." (OED website)