throw one for a loop

Question

NHK英会話上級のテキストで“It really threw me for a loop.”（本当に面食らった），“throw one for a loop.”＝「（人を）びっくりさせる」となっていたのですが，この表現の“loop”の意味が分かりません。どんな意味からこの表現が出来るのか，ご存知の方，お教え願えれば幸いです。

Riverview · Accepted Answer

The Word Detectiveの受け売りですが、分かりやすくいえば、ここでいうloopとはローラー・コースターが宙返りする、あのループ状の部分で、あそこを通るときは天地が逆さまになります。そこから、うろたえる、びっくりするという意味が出てきたようです。


詳細は下記に引用したThe Word Detectiveの記事を参照して下さい。さらに興味があれば、下記のURLからサイトまで行ってみて下さい。

Dear Word Detective: I teach a class of "native" English speakers here outside Tel Aviv. The kids do just fine with ordinary readin' and writin', but explaining idioms is a real challenge. How about some help with "thrown for a loop." I can't find anything about it in my (limited) library. -- Janet Nusbaum, via the internet.

snip
I presume that you have already explained that "thrown for a loop" means "bewildered" or "dazzled" or, less frequently, "defeated." The question is why it means that. 
The answer lies in what the Oxford English Dictionary calls, for some mysterious reason, a "centrifugal railway," but which we Americans know by the much livelier name "roller coaster." The "loop" in a roller coaster or other carnival ride is that portion of the track when the cars travel up in a circular, twisting motion so that at the apex the passengers are traveling upside down, a process also known as "looping the loop." 
It is this image of "looping the loop" that underlies "thrown for a loop," the metaphor being that some news or event is sufficiently shocking as to throw the person upside down into the air in a looping motion. This all sounds terribly dry, but you've probably seen this event demonstrated literally in hundreds of cartoons. In fact, since "thrown for a loop" first appeared in about 1923, cartoons may actually have boosted the popularity of the idiom. 
The Word Detective
URL: http://tinyurl.com/rbkex

ricanmuri · Answer

knock for a loop

Also, throw for a loop; knock down or over with a feather; knock sideways. Overcome with surprise or astonishment, as in The news of his death knocked me for a loop, or Being fired without any warning threw me for a loop, or Jane was knocked sideways when she found out she won. The first two of these hyperbolic colloquial usages, dating from the first half of the 1900s, allude to the comic-strip image of a person pushed hard enough to roll over in the shape of a loop. The third hyperbolic term, often put as You could have knocked me down with a feather, intimating that something so light as a feather could knock one down, dates from the early 1800s; the fourth was first recorded in 1925.

throwとknockの違いはあるけど起源は↑に回答されています。
英英辞書、引く習慣持たれてみては・・・？

参考URL：http://dictionary.reference.com/search?q=knock%20for%20a%20loop

throw one for a loop

The Word Detectiveの受け売りですが、分かりやすくいえば、ここでいうloopとはローラー・コースターが宙返りする、あのループ状の部分で、あそこを通るときは天地が逆さまになります。

knock for a loop

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