不意|ふいfui[0]heiban (flat)

1. na-adjective, no-adjectivesudden; abrupt; unexpected; unforeseen
   砦とりでは不意ふいに攻撃こうげきされた。↗

   The fort was attacked by surprise.

• Synonym思いがけないおもいがけないNeutralAn i-adjective for anything contrary to expectation, good or bad, as in 「思いがけないプレゼント」; 「不意」 stresses the suddenness and being caught off guard.
• Synonym唐突とうとつWrittenWritten-style word for words, actions or developments that come abruptly, as in 「唐突な質問」「唐突な結末」; 「不意」 centres on being unprepared.
• Synonym意外いがいNeutralCovers outcomes that differ from what was expected, without any sense of suddenness; 「不意」 stresses arriving so fast there is no time to prepare.
• Synonym突然とつぜんNeutralThe most common everyday word for 'sudden', usable as an adverb; 「不意」 leans written and appears mostly in 「不意に」 and 「不意を突く」.
• Synonym予想外よそうがいNeutralSays something falls outside one's predictions, often for results or figures; 「不意」 highlights being caught off guard when it happens.
• SynonymにわかNeutralCovers sudden onset as in 「俄雨」「俄に」, and also spur-of-the-moment or impromptu things; 「不意」 specifically means taking someone by surprise.
• Synonym急きゅうNeutralEveryday word for sudden or urgent things, and for steep slopes, as in 「急に」「急な坂」; 「不意」 is more written and stresses being unprepared.
• Synonym出し抜けだしぬけNeutralColloquial for doing or saying something without warning, as in 「出し抜けに質問する」; close in sense to 「不意」 but more conversational.
• Synonym卒爾そつじWrittenA written, old-fashioned word for hasty or rash behaviour; rarely used today — say 「突然」 or 「唐突」 instead.
• Synonym意想外いそうがいWrittenA rare written word for the unthinkable; in everyday speech 「意外」 or 「予想外」 is the natural choice.
• Synonym思いもよらないおもいもよらないNeutralStronger: something one could not even imagine; 「不意」 is about suddenness in time rather than the strength of the surprise.
• Synonym思わぬおもわぬNeutralA pre-noun modifier for the unexpected, as in 「思わぬ事故」; 「不意」 can also work adverbially as 「不意に」.
• SynonymひょんなCasualColloquial pre-noun word for odd, chance occurrences, as in 「ひょんなことから」; 「不意」 carries no nuance of a strange coincidence.
• Synonym予期しないよきしないNeutralSimply states that something was not anticipated in advance, often for results or situations; 「不意」 stresses the sudden, unguarded onset.
• Synonym突発的とっぱつてきNeutralDescribes accidents or incidents breaking out suddenly, as in 「突発的な事故」; 「不意」 also covers events, chiefly as 「不意に」 or 「不意を突く」.
• Synonym存外ぞんがいWrittenWritten word for 'more than expected', usually in a favourable direction, as in 「存外うまくいった」; 「不意」 is about something arriving suddenly.
• Related急激きゅうげきNeutralFor changes that are sharp and violent, as in 「急激な変化」; 「不意」 says nothing about the scale of the change.
• Related短兵急たんぺいきゅうWrittenWritten word for impetuous, hasty action, as in 「短兵急に」; 「不意」 means catching someone off guard rather than acting rashly.
• Antonym予期よきWrittenWritten word for expecting or anticipating something in advance — the very opposite of the unexpectedness of 「不意」.

For everyday 'suddenly', use 「突然」 or 「急に」. 「不意」 is the written-flavoured choice for taking someone by surprise, chiefly as 「不意に」 or 「不意を突く」. For an unexpected result pick 「意外」 or 「予想外」; for abrupt words, actions or developments, 「唐突」; for sharp changes, 「急激」. The rest are narrower or rarer: 「思いがけない」 for surprises good or bad, 「出し抜け」 and 「ひょんな」 in casual speech, 「俄」 for sudden showers or impromptu acts, and 「卒爾」「意想外」「存外」「短兵急」 as literary rarities.

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

1. 思おもいがけないこと。予期よきしないこと。予想外よそうがい。だしぬけ。またそのような様子ようす。