Emily Dickinson Lexicon

WHY, adv. [Sax. hwi, and for hwi, or for hwig, for why. Hwi, whig, coincides in elements with which. So pourquoi in French, is the same; pour and L. quid, quod; for what. The original phrase is for what, for why.]

1. For what cause or reason, interrogatively. Turn ye, turn ye, for why will ye die? – Jer. xxvii.
2. For which reason or cause, relatively. No ground of enmity, Why he should mean me ill. – Milton.
3. For what reason or cause; for which; relatively. Turn the discourse; I have a reason why I would not have you speak so tenderly. – Dryden.
4. It is used sometimes emphatically, or rather as an expletive. If her chill heart I can not move, / Why, I'll enjoy the very love. – Cowley.