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the definition for 一体【いったい】:

> Adverb : ...the heck (e.g. "what the heck?"); ...in the world (e.g. "why in
> the world?"); ...on earth (e.g. "who on earth?");
>
> —Before an interrogative, forms an emphatic question. 一体どこで彼に会ったんだ。Where on
> earth did you meet him? いったいなぜ彼を駅に連れて行ったの？Why on earth did you take him to
> the station?
>
> Noun : one object; one body; unity
>
> one form; one style one Buddhist image (or carving, etc.)
>
> Adverbial noun :
>
> generally; in general; → 一体に

Given the definition of the noun, why does this word possess an implied
incredulity when used before an interrogative?
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2012-07-01T20:46:45.990
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2012-07-01T22:59:30.553
2012-07-01T22:59:30.553
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Why does 一体 mean "what the heck?"?
> Given the definition of the noun, why does this word possess this adverbial
> meaning?

Your definition list is incomplete. Another sense means "the whole",
"entirety", "general". This sense--while still a noun--is used like an adverb
and may be accompanied with に, such as 一体に今年は寒かった. It is from this usage that
the adverbial sense derived. Adverbially, the meaning changes to "on the
whole", "in general", "in short" etc. Adverbial quote: 一体生徒が全然悪いです (Sōseki,
Botchan*) When used in a question, it emphasizes the questioner’s feelings,
which you are translating as "what the heck".

  * Note: This is a famous, well-known quote with 全然 + non-negative predicate.
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2012-07-01T22:28:47.550
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2012-07-01T22:28:47.550
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answer