Oxford English Dictionary Online. You have to subscribe to OED to use the service which is updated quarterly with at least 1000 new and revised entries
Site Hits: 83 today, 225 yesterday, 5,720 this month, 5,984 last month, 552,341 total System Hits: 16,837 today, 112,270 yesterday, 3,901,201 this month, 4,104,428 last month, 1,589,537,298 total