<p><strong>Adverb</strong></p><ul><li>For what? For what reason, cause, or purpose?</li><li>Example: Why did you behave so badly?</li></ul><p><strong>Conjunction</strong></p><ul><li>For what cause or reason: I don't know why he is leaving.</li><li>For which; on account of which (usually after "reason" to introduce a relative clause): the reason why he refused to go.</li><li>The reason for which: That is why he returned.</li></ul><p><strong>Noun</strong></p><ul><li>Plural: whys.</li><li>A question concerning the cause or reason for which something is done, achieved, etc.: a child's unending hows and whys.</li><li>The cause or reason: the whys and wherefores of a troublesome situation.</li></ul><p><strong>Interjection</strong></p><ul><li>Used as an expression of surprise, hesitation, etc., or sometimes a mere expletive: Why, it's all gone!</li></ul>