〜とは

Meaning

There are two usages. One is the form 「まさか〜とは」, expressing surprise or exclamation at an unexpected fact. In this usage, the sentence is sometimes left unfinished at the end, as in 「あの人が優勝するとは」, leaving a lingering sense of surprise. The other is the form 「〜とは…のことだ」, used to explain or define the meaning of a certain word.

Examples

あの真面目な彼が、まさか遅刻するとは思わなかった。 I never thought someone as serious as him would be late.
こんな所で偶然会うとは、驚いた。 What a surprise to run into you in a place like this.
「過半数」とは、全体の半分を超える数のことだ。 Kahansuu means a number exceeding half of the total.
あれほど練習した彼が、よもや初戦で敗れるとは。 He who had practiced so much—who would have thought he'd lose in the very first match.