Definition of unless conjunction from the Oxford Advanced Learner's Dictionary

      

    unless

     conjunction
    conjunction
    BrE BrE//ənˈles//
     
    ; NAmE NAmE//ənˈles//
     
     
    jump to other results
  1. 1  used to say that something can only happen or be true in a particular situation You won't get paid for time off unless you have a doctor's note. I won't tell them—not unless you say I can. Unless I'm mistaken, she was back at work yesterday. He hasn't got any hobbies—unless you call watching TV a hobby.
  2. 2  used to give the only situation in which something will not happen or be true I sleep with the window open unless it's really cold. Unless something unexpected happens, I'll see you tomorrow. Have a cup of tea—unless you'd prefer a cold drink?
  3. Unless is used to talk about a situation that could happen, or something that could be true, in the future. If you know that something has not happened or that something is not true, use if… notIf you weren't always in such a hurry (= but you are), your work would be much better.Your work would be much better unless you were always in such a hurry.
    Word Origin late Middle English: from on or in (assimilated through lack of stress to un-) + less.
See the Oxford Advanced American Dictionary entry: unless