OED: Oxford English Dictionary (Oxford University Press) This link opens in a new window"The Oxford English Dictionary (OED) is widely regarded as the accepted authority on the English language. It is an unsurpassed guide to the meaning, history, and pronunciation of 600,000 words— past and present—from across the English-speaking world."
The 20-volume print set is available in the Main Library Reference -- PE1625.M7 1989.