\When\, adv. [OE. when, whan, whenne, whanne, AS.
hw[ae]nne, hwanne, hwonne; akin to OS. hwan, OD. wan, OHG.
wanne, G. wann when, wenn if, when, Goth. hwan when, and to
E. who. ????. See {Who}.]
1. At what time; -- used interrogatively.
         When shall these things be?           --Matt. xxiv.
                                               3.
Note: See the Note under {What}, pron., 1.
2. At what time; at, during, or after the time that; at or
   just after, the moment that; -- used relatively.
         Kings may Take their advantage when and how they
         list.                                 --Daniel.
         Book lore ne'er served, when trial came, Nor gifts,
         when faith was dead.                  --J. H.
                                               Newman.
3. While; whereas; although; -- used in the manner of a
   conjunction to introduce a dependent adverbial sentence or
   clause, having a causal, conditional, or adversative
   relation to the principal proposition; as, he chose to
   turn highwayman when he might have continued an honest
   man; he removed the tree when it was the best in the
   grounds.
4. Which time; then; -- used elliptically as a noun.
         I was adopted heir by his consent; Since when, his
         oath is broke.                        --Shak.
Note: When was formerly used as an exclamation of surprise or
      impatience, like what!
            Come hither; mend my ruff: Here, when! thou art
            such a tedious lady!               --J. Webster.
{When as}, {When that}, at the time that; when. [Obs.]
         When as sacred light began to dawn.   --Milton.
         When that mine eye is famished for a look. --Shak.