Happening abruptly or unexpectedly; sudden and unforeseen (also used adverbially).
突然の雨でピクニックは中止になった。
The picnic was canceled due to a sudden rain shower.
彼は会議の途中で突然辞表を出した。
He suddenly submitted his resignation during the meeting.
話が突然変わって驚いた。
I was surprised when the topic suddenly changed.