—adv. for what? for what reason, cause, or purpose?: Why did you behave so badly?
—conj. 1. for what cause or reason: I don't know why he is leaving. 2. for which; on account of which (usually after reason to introduce a relative clause): the reason why he refused to go. 3. the reason for which: That is why he returned.
—n. 1. a question concerning the cause or reason for which something is done, achieved, etc.: a child's unending hows and whys. 2. the cause or reason: the whys and wherefores of a troublesome situation.
—interj. (used as an expression of surprise, hesitation, etc., or sometimes a mere expletive): Why, it's all gone!