unless

UK: /ʌnˈlɛs/ US: /ʌnˈlɛs/ ,(un les′, ən-)

WordReference Random House Learner's Dictionary of American English © 2026

un•less /ʌnˈlɛs/   conj. 

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

WordReference Random House Unabridged Dictionary of American English © 2026

un•less  (un les′, ən-), conj. 

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

prep. 

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

• 1400–50; late Middle English prepositional phrase on less (also o less(e), earlier upon less) on a lesser footing or condition (than); first used as a preposition and conj. in the early 16th century; see on, less

Collins Concise English Dictionary © HarperCollins Publishers::

unless / ʌnˈlɛs/ conjunction

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

Etymology: 14th Century: onlesse, from on on + lesse less; compare French à moins que, literally: at less than