For what cause, reason, or purpose; on what account; wherefore; -- used interrogatively. See the Note under What, pron., 1.
- For what purpose, reason, or cause; with what intention, justification, or motive: Why is the door shut? Why do birds sing?
- The reason, cause, or purpose for which: I know why you left.
- Usage Problem On account of which; for which: "The reason why [regular verbs] are called regular is that we can predict what all the other three forms are” ( Randolph Quirk).
- The cause or intention underlying a given action or situation: studying the whys of antisocial behavior.
- A difficult problem or question.
- Used to express mild surprise, indignation, or impatience.