The online version of the classic dictionary. An unsurpassed guide to the meaning, history, and pronunciation of over half a million words, both present and past. It traces the usage of words through 2.5 million quotations from a wide range of international English language sources, from classic literature and specialist periodicals to film scripts and cook books.
Below are key reference books that provide a general overview of a topic or help identify synonyms, related terms, or basic data. These sources often include references and lists of further readings.
The Harvard Concordance to Shakespeare by 
A Shakespeare Glossary by 
Biblical References in Shakespeare's Plays by 
Shakespeare A to Z: The Essential Reference to His Plays, His Poems, His Life and Times, and More by 
All Things Shakespeare: An Encyclopedia of Shakespeare's World by 
Shakespeares after Shakespeare: An Encyclopedia of the Bard in Mass Media and Popular Culture by 
The Columbia Encyclopedia of Modern Drama by Authoritative guide to Shakespeare's plays and poems, and their interpretation around the world over the last four centuries. Special feature entries on every play are included.
Offers succinct, focused articles that provide an overview of literary theory from a twentieth-century Western perspective.
From the Open Source Shakespeare website by Eric M. Johnson.
