どんどん
どんどん · dondon · JLPT N4 · adverb
quickly and steadily
🥁 don-don = a drum beat that keeps coming, one hit after another
どん is the Japanese sound word for a drum thud. Doubling it gives a nonstop beat: don, don, don. Anything that moves ahead at that pace, with no pause between hits, is going どんどん: fast, steady, without letting up.