adverb
with a gasp; in surprise; with a shout
Describes a sudden reaction of surprise, shock, or amazement, often accompanied by an exclamation. Frequently used in the set phrase あっと驚く.
See also: あっと驚く
その知らせを聞いて、彼はあっと驚いた。
He gasped in surprise when he heard the news.
あっと言う間に時間が過ぎた。
Time flew by in the blink of an eye.