Nisi | Webster's Dictionary of the English Language

nisi
nĭ-sĭ (archaic forms nisei and nise, Lex Rubria, v. Ritschl, Legis Rubriae pars superstes, Bonnae,...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
nisi
nisi conj. 1 ne+si, if not, unless : nomen iudicum amittemus, nisi hic ex ipsis causis ...

An Elementary Latin Dictionary