* Except on a specified condition; if not.
_I’m leaving UNLESS I get a pay rise (AmE: raise)._
* 1839, Denison Olmsted, _A Compendium of Astronomy_ Page 95
Secondly, When a body is once in motion it will continue to move forever, UNLESS something stops it. When a ball is struck on the surface of the earth, the friction of the earth and the resistance of the air soon stop its motion.
* (except on a condition): if
* precisely unless
* unless and until, until and unless