I stumbled across a yojijukogo...

[bloritsch]

一体全体

It was in the sentence (splattered across the side of a car):

一体全体こころって何でしょう。
What on earth is the heart, I wonder.

Yes, both English and Japanese were spelled out for you.

Any ideas on where the phrase come from? Politeness level? The yojijukogo lessons have me wondering about other phrases that haven't been covered yet. It seems that this phrase could be less than polite, but I'm not sure.

[Javizy]

Can't answer your question, but if you've got a fairly decent level of Japanese, check out this 四字熟語 dictionary. There's also a cool 四字熟語 game if you fancy a challenge

[Psy]

This is simply a stronger way of asking something with いったい. The dictionary definition:

（副）
「一体(1)」を強めた言い方。強い疑問や詰問の時多く使う。

(fuku)
"ittai (1)" wo tsuyometa iikata. tsuyoi gimon ya kitsumon no toki ooku tsukau.

(adv)
A more emphasized ["ittai"(1)]. Often used during strong questioning or cross-examination.

As for politeness levels, I'd be careful with this one since it's awfully direct.

And Javizy, I checked out that site-- though I was able to guess most of them (in 初級 and 中級, forget 上級) through knowing the characters, it serves as a great reminder that I need to study more of these.