訓 つ(く) ・ 音 トツ,カ
漢越音: đột
Hole 穴 over 大 (originally 犬, dog): a dog suddenly bursting out of its den, so it means thrust or sudden (Han Viet dot, as in dot nhien = suddenly).
Stroke data: KanjiVG (CC BY-SA 3.0) — kanjivg.tagaini.net
突然、雨が降り出しました。 (とつぜんあめがふりだしました)
Suddenly it started to rain.