Definition of: when

(hwen) adverb
1. Interrogatively, at what or which time: When did you arrive?
2. Conjunctively: a At which: the time when we went on the picnic. b At which or what time: They watched till midnight when they fell asleep. c As soon as: He laughed when he heard it; You may play when you finish work. d Although: He walks when he might ride. e At the time that; while: when you were in church; when we were young. f If; considering that: When in doubt, ask; How can I buy it when I have no money? g After which; then: We had just awakened when you called.
—pron. What or which time: since when; till when.
—noun The time; date: I don't know the when or the circumstances. [OE hwanne, hwænne]