Why (?), adv. [OE. whi, why, AS. hwi, hw, instrumental case of hwa, hwaet; akin to Icel. hvi why, Dan. & Sw. hvi; cf. Goth. hw. . 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.
Why is sometimes used as an interjection or an expletive in expression of surprise or content at a turn of affairs; used also in calling. "Why, Jessica!"
Shak.
If her chill heart I can not move,
Why, I'll enjoy the very love.
Cowley.
Sometimes, also, it is used as a noun.
The how and the why and the where.
Goldsmith.
For why, because; why. See Forwhy. [Obs. or Colloq.]
© Webster 1913.
Why, n. A young heifer. [Prov. Eng.]
Grose.
© Webster 1913. | 
