unless

[ uhn-les, uh n- ]
/ ʌnˈlɛs, ən- /

conjunction

except under the circumstances that: I'll be there at nine, unless the train is late.

preposition

except; but; save: Nothing will come of it, unless disaster.

Origin of unless

1400–50; late ME prepositional phrase on less (also o less(e), earlier upon less) on a lesser footing or condition (than); first used as a preposition and conjunction in the early 16th century; see on, less
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Examples from the Web for unless

British Dictionary definitions for unless

unless

/ (ʌnˈlɛs) /

conjunction

(subordinating) except under the circumstances that; except on the condition thatthey'll sell it unless he hears otherwise

preposition

rare except

Word Origin for unless

C14: onlesse, from on on + lesse less; compare French à moins que, literally: at less than
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012