The Oxford English Dictionary (OED Online) is the major source of scholarship on words and sources in the English language.
Oxford Dictionaries is a new service which brings together the prestigious language dictionaries published by Oxford University Press. We subscribe to a number of bilingual dictionaries: French, German, Italian, Russian, and Spanish. You can search language dictionaries via the search bar at the top of every page, or discover quizzes, blog posts, and grammar help for each language by using the selector in the top right hand side of the page. Create a free account and receive a Word of the Day and newsletter.
The Oxford Dictionary of National Biography is the online version of the major reference work for information about people from British history and culture.
To find out what resources are available for other subjects look at Oxford Reference.