The word "abridge," is a verb that means to condense or reduce. In other words, to abridge is to take something long and make it short. "Unabridged" denotes that something exists in its complete form and has not been abridged and only takes one grammatical form, the adjective. Both words derive from the old French verb "abregier," which means to shorten, originating from the Latin word "abbreviare," meaning "to abbreviate."
The word "abridge" most often applies to books. Because the English language contains so many words, most dictionary publishers sell abridged dictionaries, or desk dictionaries, that define approximately 200,000 commonly-used words. Unabridged dictionaries often number multiple volumes, such as "The Oxford English Dictionary," which boasts 20 volumes. Sometimes publishers release abridged versions of long novels, such as those by Charles Dickens. Some audio books are also available in abridged formats.
Publishers abridge books for the sake of convenience and interest. Unabridged dictionaries are simply not practical for the average person who needs an occasional reference tool. People who might not normally sit down with a 1,000-page Dickens novel might find an abridged version more accessible. However, scholars rely on unabridged editions of works. Some unabridged dictionaries also include the history of a word, an area of interest to an etymologist or linguist. One more reason publishers release abridged editions of books is to censor controversial scenes, such as those portraying overt sexuality, expletives or violence.
Aside from the dictionary, many books have been abridged, most often for censorship reasons. Otto Frank withheld several entries from "The Diary of Anne Frank" that dealt with his daughter's sexuality for many years. D.H. Lawrence's sexually explicit novel, "Lady Chatterley's Lover," was also abridged for the purposes of censorship. Thomas Bowdler removed crude phrases in his editions of Shakespeare, resulting in the term "bowdlerize."