a legal phrase derived from an ancient writ in which the words occur. Previously to the statute of Westminster 2, trials by assizes or juries could only take place where the king happened to reside, or before the justices on their septennial circuit through the English counties; but by 13th Edw. I., cap. 30, the judges were directed to hold certain assizes in every county not oftener than three times in every year. The statute required that the day and place in the county in which a case was to be tried should be specified in the writ which assembled the jury. Instead, accordingly, of the old writ, commanding the sheriff to bring the jury to Westminster to try the cause, a nisi prius clause was added to the writ as follows:—"We command you, that you cause to come before our justices at Westminster, on the morrow of All Souls, twelve lawful men, who, &c., unless before (nisi prius) that day A. B. and C. D., our justices assigned for that purpose, shall come to your county to take the assizes there." The day of summons to Westminster is always arranged to be later than the day for taking the county assize, and hence the cause is always tried before the date at which the sheriff is commanded to return the jury to Westminster. In time, the phrase nisi prius came to be applied to a large class of judicial business transacted at the several assizes throughout the country before judges of the superior courts. Judges of assize are called judges of nisi prius; they are said to be sitting at nisi prius, when sitting alone to try causes, and the law by which their decisions are regulated is called the law of nisi prius.