Webster's Revised Unabridged Dictionary · 1913

Why

Why , adverb

[Old English whi, why, Anglo-Saxon hwī, hw{not transcribed}, instrumental case of hwā, hwat; akin to Icelandic hvī why, Danish & Swedish hvi; compare Gothic hw{not transcribed}. {not transcribed}. See Who.]

1.
For what cause, reason, or purpose; on what account; wherefore; -- used interrogatively. See the Note under What, pron., 1.
Turn ye, turn ye from your evil ways; for why will ye die, O house of Israel? — Ezek. xxxiii. 11
2.
For which; on account of which; -- used relatively.
No ground of enmity between us known Why he should mean me ill or seek to harm. — Milton
Turn the discourse; I have a reason why I would not have you speak so tenderly. — Dryden
3.
The reason or cause for which; that on account of which; on what account; as, I know not why he left town so suddenly; -- used as a compound relative.
If her chill heart I can not move, Why, I'll enjoy the very love. — Cowley
The how and the why and the where. — Goldsmith
Collocations (1)
For why , because; why. See Forwhy. [Obsolete or Colloquial]

Why , noun

A young heifer. [Provincial English] — Grose