The two most commonly used legal dictionaries are Black's Law Dictionary and Ballentine's Law Dictionary. Print copies of Black's are located on dictionary stands on the fourth and fifth floors.
Although not technically a legal dictionary, Words and Phrases also provides definitions of legal terms. Whereas legal dictionaries provide definitions taken from a variety of sources, Words and Phrases provides definitions taken almost exclusively from court opinions. This resource can be invaluable in helping you determine a specific court's interpretation of a legal term.
Don't forget general dictionaries, which provide information about the etymology and use of a term in addition to the definition. The unabridged edition of the Oxford English Dictionary is considered the authoritative dictionary of the English language. Also available in the Law Library are Shorter Oxford English Dictionary and the American Heritage Dictionary of the English Language.