expression, godan verb (-ku)
be astonished; get a big surprise; be taken aback
Expresses a sudden, strong surprise; often used when something unexpected happens and you react with a gasp or a start.
突然の大きな音にあっと驚いた。
I was startled by the sudden loud noise.
彼の変わりように
I was astonished by how much he had changed.