How to say "speedy" in Japanese

• スピーディーCommon
  na-adjectiveThe direct borrowing of English 'speedy'. It covers the promptness sense — a person or organization dealing with work briskly and efficiently — rather than the speed of a moving object.
• 速やかすみやかCommon
  na-adjectiveCovers the 'prompt' sense: doing something quickly, without delay. It typically appears in instructions, requests, or announcements urging that something be done promptly.
  決定けっていの後あとすみやかに実行じっこうに移うつして欲ほしい。↗

  I want quick action subsequent to the decision.
• 早いはやいJLPT N5approx.Common
  i-adjectiveThe plain adjective for speed itself: when 'speedy' just means fast — a speedy car, a speedy runner — this is the word, describing how quickly something moves or happens.
  子供こどもは成長せいちょうが早はやい。↗

  Children grow very quickly.
• 迅速じんそくJLPT N1approx.Common
  na-adjective, nounFor 'speedy' in the sense of rapid handling — quick responses, quick processing, quick service. It stresses that a matter is dealt with promptly and without wasted time.
  間髪かんぱつを入いれず、迅速じんそくかつ的確てきかくな応対おうたい、畏れ入おそれいります。↗

  Such an accurate, lightning-quick reply. What can I say?

For plain speed of movement or occurrence use 「早い」; for promptness in getting things done, choose 「スピーディー」 (the loanword), 「速やか」 (acting without delay, as in instructions), or 迅速 (rapid handling of responses and procedures).

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

• スピーディーspeedy
• 速やかすみやかquick
• 早いはやいfast
• 迅速じんそく(very) quick
• 一日も早いいちにちもはやいspeedy