唖然 あぜん
azen

Taru Adjective
To-Adverb

1. dumbfounded; speechless; flabbergasted; struck dumb with astonishment

彼女 かのじょはその らせに唖然 あぜんとした。
kanojowa sono shiraseni azento shita.
She was struck dumb at the news.
Other forms: