How to say "rapidly" in Japanese

• メキメキCommon
  adverb (with と)Covers 'rapidly' in the sense of making remarkable, visible progress, especially improvement in skill or condition. Its mimetic character adds a nuance of change that others can plainly observe.
  タケシはめきめき数学すうがくの力ちからをつけている。↗

  Takeshi is making great progress with math.
• 急にきゅうにJLPT N3approx.Common
  adverbThis means 'rapidly' only in the sense of something happening suddenly or without warning; it is really 'suddenly' or 'all at once'. Use it when speed implies abruptness, not steady fast motion.
  気苦労きぐろうで彼かれは急きゅうにふけた。↗

  Care aged him quickly.
• パッとCommon
  adverbDescribes rapid action done in a flash, with a sudden, snappy movement or change. A mimetic word, it suits things that are over in an instant rather than processes that continue quickly.
  レース中ちゅうにその車くるまはぱっと燃え上もえあがった。↗

  The car burned up in the race.
• どんどんJLPT N4approx.Common
  adverb (with と)The usual choice for 'rapidly' as steady, accelerating progress — things advancing or increasing one after another, such as growth or expansion. Its mimetic rhythm suggests continuous forward momentum.
  ある種しゅの動物どうぶつはどんどん数かずが減へってきている。↗

  Certain animals are fast disappearing.
• 早くはやくCommon
  adverbThe plain adverb for doing something fast or quickly; 'rapidly' in the simple sense of high speed. Use it whenever you just need to say an action is performed quickly, with no special nuance.

Choose based on manner: 「どんどん」 for steady ongoing progress, 「メキメキ」 for marked visible improvement, 「急に」 and 「パッと」 for sudden speed, and 「早く」 for plain speed of action.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• めきめきremarkably
• 急にきゅうにswiftly
• パッとsuddenly
• ぐんぐんrapidly
• ずんずんrapidly
• とみにsuddenly
• ばっとsuddenly
• 駸々しんしんproceeding quickly
• 快快的カイカイデhurriedly
• ぐぐっとwith a burst of strength
• すくすく(growing) quickly (esp. children, plants)
• どんどんrapidly
• 早くはやくquickly
• じゃんじゃんcontinuously
• にょきにょき(growing) rapidly