When

At what time; -- used interrogatively.

At what time; at, during, or after the time that; at or just after, the moment that; -- used relatively.

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.

Which time; then; -- used elliptically as a noun.