'NISI' definitions:

Definition of 'nisi'

adjective

Not final or absolute; "the decree is nisi and not absolute"

From: GCIDE

Nisi \Ni"si\, conj. [L.] Unless; if not; -- used mostly in law. [1913 Webster]
Note: In legal proceedings, this word is used to indicate that any order, etc., shall take effect at a given time, unless before that time the order, etc., in modified, or something else is done to prevent its taking effect. Continuance nisi is a conditional continuance of the case till the next term of the court, unless otherwise disposed of in the mean time. [1913 Webster]
Nisi prius (Law), unless before; -- a phrase applied to terms of court, held generally by a single judge, with a jury, for the trial of civil causes. The term originated in a legal fiction. An issue of fact being made up, it is, according to the English practice, appointed by the entry on the record, or written proceedings, to be tried by a jury from the county of which the proceedings are dated, at Westminster, unless before the day appointed (nisi prius) the judges shall have come to the county in question (which they always do) and there try the cause. See In banc, under Banc. [1913 Webster]