when

 
Pronunciation: /wɛn/

interrogative adverb

  • at what time: when did you last see him? [with preposition]: since when have you been interested?
  • how soon: when can I see you?
  • in what circumstances: when would such a rule be justifiable?

relative adverb

  • at or on which (referring to a time or circumstance): Saturday is the day when I get my hair done

conjunction

  • 1at or during the time that: I loved maths when I was at school
  • after: call me when you’ve finished
  • at any time that; whenever: can you spare five minutes when it’s convenient?
  • 2after which; and just then (implying suddenness): he had just drifted off to sleep when the phone rang
  • 3in view of the fact that; considering that: why bother to paint it when you can photograph it with the same effect?
  • 4although; whereas: I’m saying it now when I should have told you long ago

Origin:

Old English hwanne, hwenne; of Germanic origin; related to German wenn 'if', wann 'when'

Grammar

The main uses of when are: question word: When did you iast see your father? relative pronoun: I cannot recall an occasion when he asked me for help before. subordinating conjunction introducing a noun clause: I haven’t told them when I start. subordinating conjunction introducing an adverbial clause of time: The off-season hotel had been empty when she arrived.