What it means
まさか expresses strong disbelief, surprise, or the speaker’s conviction that a situation is impossible. It is often used before a negative or unexpected proposition and can mean “no way,” “surely not,” or “I never imagined that.” The exact translation depends on the following statement and the speaker’s tone.
Usage note
まさか is not a plain–polite inflection pair, so it remains unchanged in polite sentences. Do not translate it as “no way” in every context; before an unexpected affirmative statement, it can instead express shocked disbelief or that the speaker never imagined something.
Example sentences
まさか、明日の試験が中止になるとは思いませんでした。
No way, I never imagined that tomorrow's exam would be canceled.
まさか田中さんが海外へ引っ越すとは、誰も予想していませんでした。
No one expected that Mr. Tanaka would move abroad.
まさかこの古い時計がまだ動くとは思わなかった。
I never imagined that this old clock would still work.