Occurring suddenly or unexpectedly, often causing surprise or alarm.
不意に友人が部屋に入ってきて驚いた。
A friend unexpectedly came into the room and I was surprised.
彼は不意に質問を振られて答えに詰まった。
He was asked a question out of the blue and was at a loss for an answer.
不意に電話が鳴ったので出られなかった。
The phone rang unexpectedly so I couldn't pick up.