The CWU James E. Brooks Library has a lot of wonderful databases*, including the Oxford University Press's Oxford Reference Online - which does indeed contain a digital version of The Oxford Dictionary of English. There is no central authority for the English language, but everyone agrees that an OED usage is a correct usage.* You can reach these databases from off-campus using your last name (as it appears on your ID card) and your ID number (with a 0 in front of it).

For the more prosaic, here is the American Heritage Dictionary, and the classic Roget's Thesaurus (aka Bartleby.com)