まさか
No way, I never thoughtmachine translation
Formationまさか + 〜とは思わなかった／〜ないだろう; stands alone as an exclamation
まさか expresses DISBELIEF at a possibility or event: まさか彼が優勝するとは思わなかった (I never thought he would win the championship). The most common frame is まさか〜とは思わなかった — "I never imagined that…," used when something unbelievable has become fact.
When it has NOT yet happened, まさか pairs with a negative conjecture to say "surely not…": まさか雪は降らないだろう (surely it won't snow). And in conversation, まさか standing alone is a complete exclamation: 「まさか！」 (No way!).
Grouping it with its exclamatory relatives: いったい emphasizes the QUESTION "what on earth…," while まさか stresses the DISBELIEF at an event. なんて at the end of a sentence also expresses astonishment, so the pair まさか〜なんて (to think that… would happen!) is a very natural Japanese way to cry out in dismay.
Examples
まさか彼が優勝するとは思いませんでした。
I never thought he would win the championship.
まさか、こんな所で先生に会うなんて。
I can't believe I'd run into my teacher in a place like this.
まさか雪は降らないだろうと思って、コートを持って来ませんでした。
I figured it surely wouldn't snow, so I didn't bring a coat.