突然|とつぜんtotsuzen[0]heiban (flat)

1. no-adjective, na-adjective, adverbabrupt; sudden; unexpected
   すべて突然とつぜん起おこった。↗

   Everything happened all at once.

• Synonym突如とつじょWrittenWritten/formal prose, common in news and novels, as in 「突如として現れる」; 「突然」 is used freely in both speech and writing.
• Synonym不意にふいにNeutralAn adverb stressing that something catches you off guard; 「突然」 is more versatile and can also work as a na-adjective.
• SynonymにわかにWrittenWritten/formal prose, for a situation changing all at once, as in 「にわかに曇る」; 「突然」 is the more everyday choice.
• Synonym急にきゅうにNeutralThe most common choice in speech; it also covers quick or sharp change. 「突然」 stresses that there was no warning.
• SynonymパッとCasualA mimetic word for something spreading in a flash or a swift action; 「突然」 stresses the lack of warning.
• Synonym急きゅうNeutralA na-adjective common in speech that also covers urgent or steep, as in 「急な用事」; 「突然」 stresses the lack of warning.
• SynonymいきなりNeutralCommon in speech, for something happening with no lead-up, as in 「いきなり殴る」 or 「いきなり雨が降り出す」; 「突然」 is more objective and versatile.
• SynonymたちまちNeutralFor reaching a state in the blink of an eye, as in 「たちまち売り切れる」; 「突然」 is about events happening.
• Synonym唐突とうとつNeutralFor remarks or behavior that feel abrupt or out of place, as in 「唐突な質問」; 「突然」 broadly covers anything happening without warning or unexpectedly.
• Synonym不意ふいNeutralFor the unexpected, mostly in set uses like 「不意を突く」 and 「不意の来客」; 「突然」 stresses that things happen suddenly.
• SynonymにわかNeutralA na-adjective for things happening all at once, as in 「にわか雨」; it also means a bandwagon fan, a sense common in speech.
• RelatedふとNeutralMostly for thoughts or glances arising unbidden, as in 「ふと思い出す」; 「突然」 is about events happening suddenly.
• RelatedさっとNeutralFor brisk, nimble action, or wind and rain springing up; 「突然」 stresses the absence of warning.
• Related急激きゅうげきNeutralDescribes change that is both fast and intense, as in 「急激な変化」; 「突然」 stresses the absence of warning.
• Related予想外よそうがいNeutralStresses that a result differs from what was expected, as in 「予想外の結果」; 「突然」 stresses no warning in timing.
• Related出し抜けだしぬけCasualColloquial, for catching someone cold with something abrupt; 「突然」 is more neutral.
• RelatedやにわにWrittenWritten/formal prose, for acting on the spot at once or without warning; mostly modifies a person's actions.
• RelatedとみにWrittenWritten/formal prose, for a degree changing markedly at once, as in 「とみに衰える」; 「突然」 is about events happening.
• RelatedふいとCasualColloquial, for doing something abruptly, unexpectedly or on a whim, as in 「ふいと出て行く」; mostly modifies people's actions.
• Related突発的とっぱつてきWrittenA na-adjective for events or accidents breaking out unexpectedly; 「突然」 is more versatile.
• Related忽然こつぜんWrittenWritten/formal prose, mostly for things appearing or vanishing, as in 「忽然と姿を消す」; 「突然」 is more versatile.
• RelatedふっとNeutralColloquial, for something happening unbidden in a flash, often with verbs like remembering or vanishing; 「突然」 is more objective.
• RelatedつとWrittenAn old-fashioned word for rising or moving with a quick jerk; rarely heard in modern Japanese.
• RelatedついとNeutralFor a light, quick movement, as in 「ついと立ち去る」; carries a literary flavor.
• RelatedひょいとCasualColloquial, for a light, quick movement or turning up offhand, as in 「ひょいと現れる」.
• Related図らずもはからずもWrittenWritten/formal prose, for something happening unexpectedly or unintentionally, as in 「はからずも優勝した」; not necessarily against one's wishes. 「突然」 stresses no warning.
• Antonym徐々にじょじょにNeutralThe antonym in manner of change: it means gradually, little by little.
• Antonym漸次ぜんじWrittenWritten/formal prose antonym in manner of change: it means step by step, gradually.

Use 「突然」 for anything that happens with no warning; it works in both speech and writing. In everyday talk 「急に」 and 「いきなり」 are the natural picks, while 「突如」 and 「にわかに」 suit written prose. For thoughts that pop up unbidden, use 「ふと」; for remarks or behavior that feel abrupt, 「唐突」. The others are narrower: 「パッと」 for swift motion, 「不意」 for the unexpected, and 「徐々に」 as the gradual opposite.

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

1. ある事象じしょうが、予見よけんや兆候ちょうこうといったものがなく発生はっせいする様子ようす。だしぬけ。
2. ある事象じしょうが、予見よけんや兆候ちょうこうといったものがなく発生はっせいする様子ようす。急きゅうに。突如とつじょ。