unless

conjunction

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

preposition

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

conjunction

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

preposition

2. rare except

conj.mid-15c., earlier onlesse, from on lesse (than) “on a less condition (than),” the first syllable originally on, but the negative connotation and the lack of stress changed it to un-.