From WordNet (r) 2.0 (August 2003) [wn]:
why
n : the cause or intention underlying an action or situation,
especially in the phrase `the whys and wherefores' [syn:
wherefore]
adv : question word; what is the reason (`how come' is a
nonstandard variant); "why are you here?"; "how come he
got an ice cream cone but I didn't?" [syn: how come]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Why \Why\, adv. [OE. whi, why, AS. hw[imac], hw?, instrumental
case of hw[=a], hw[ae]t; akin to Icel. hv[imac] why, Dan. &
Sw. hvi; cf. Goth. hw?. ?. See Who.]
[1913 Webster]
1. For what cause, reason, or purpose; on what account;
wherefore; -- used interrogatively. See the Note under
What, pron., 1.
[1913 Webster]
Turn ye, turn ye from your evil ways; for why will
ye die, O house of Israel? --Ezek.
xxxiii. 11.
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2. For which; on account of which; -- used relatively.
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No ground of enmity between us known
Why he should mean me ill or seek to harm. --Milton.
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Turn the discourse; I have a reason why
I would not have you speak so tenderly. --Dryden.
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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.
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Note: 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.
[1913 Webster]
If her chill heart I can not move,
Why, I'll enjoy the very love. --Cowley.
[1913 Webster] Sometimes, also, it is used as a noun.
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The how and the why and the where. --Goldsmith.
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For why, because; why. See Forwhy. [Obs. or Colloq.]
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From The Collaborative International Dictionary of English v.0.48 [gcide]:
Why \Why\, n.
A young heifer. [Prov. Eng.] --Grose.
[1913 Webster] Whydah bird