Latinnisiprius(“unless previously”), from the first two words of the old Latin writ summoning the juries to appear at Westminster unless, before the day appointed, the judges had come to the county.
Noun
nisi prius (uncountable)
(law,historical) In the 19th century, those legal actionstried before judges of the King's Bench Division, and in the early 20th century those actions tried at assize by a judge given a commission.