A legal dictionary contains the definitions of legal terms taken from a variety of sources. They are the first place you should look when you do not understand what a legal term means.
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. For online access, find Black's on Westlaw, and Ballentine's on Lexis.
In addition to providing a general definition of the legal term in question, legal dictionaries may also provide references to applicable primary law and other secondary sources containing more in-depth discussions of the term. For example, the entry for the legal term of art in Black's Law Dictionary contains a definition and references two Supreme Court opinions.
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. Find Words and Phrases on Westlaw.
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 available online and is considered the authoritative dictionary of the English language. Available in the Law Library are Shorter Oxford English Dictionary and the American Heritage Dictionary of the English Language.