Depending on how versed you are in law, a legal dictionary may be the first secondary source you need before tackling your legal query. Aside from basic English legal jargon, American law still contains Latin phrases, which need specific translations.
For example, our writ of certiorari - through which the Supreme Court decides to review lower courts’ decisions - comes from the Latin certiorari. According to Black’s Law Dictionary, arguably the best legal dictionary of American law, and available on Westlaw, certiorari means “to be more fully informed.”

Whether knowing its Latin meaning helps you understand how the institution functions may be arguable. Nevertheless, using a legal dictionary, if it becomes a habit, may help you stay focused and avoid desperate moments of unnecessary confusion.

Aside from Black’s Law Dictionary, there are other legal language reference works. Some of them are more modest in content. They are focused on a specific legal area, such as Lee’s Dictionary of Environmental Legal Terms, which defines the terms according to the specific environmental legal rule that contains them. For example, “acid rain program” is defined according to the administrative regulation that established it, 40 G.F.R. Section 72.2 (2002), as “the national sulfur dioxide and nitrogen oxides air pollution control and emissions reduction program.”