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

      

    when

     conjunction
    conjunction
    BrE BrE//wen//
     
    ; NAmE NAmE//wen//
     
     
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  1. 1  at or during the time that I loved history when I was at school.
  2. 2  after Call me when you've finished.
  3. 3  at any time that; whenever Can you spare five minutes when it's convenient?
  4. 4  just after which He had just drifted off to sleep when the phone rang.
  5. 5  considering that How can they expect to learn anything when they never listen?
  6. 6although She claimed to be 18, when I know she's only 16.
  7. Word Origin Old English hwanne, hwenne; of Germanic origin; related to German wenn ‘if’, wann ‘when’.Idioms used to say that something may happen at some time in the future, but only when something else has happened We'll decide on the team as and when we qualify. I'll tell you more as and when (= as soon as I can).
See the Oxford Advanced American Dictionary entry: when