不定|ふていfutei[0]heiban (flat)

1. no-adjective, na-adjectiveunsettled; uncertain; indefinite; unfixed; variable; irregular; changeable
2. no-adjective, mathindeterminate

• Synonym不確定ふかくていWrittenWritten/formal. Says something has not been pinned down, as in 「不確定要素」; 「不定」 stresses being unfixed and apt to change.
• Synonym未定みていNeutralNeutral. Means not yet decided, as in 「日程未定」; 「不定」 describes something inherently unfixed, as in 「住所不定」.
• Synonym未確定みかくていWrittenWritten/formal. Says something has not yet been settled or confirmed; 「不定」 describes something inherently unfixed.
• Synonym未決定みけっていWrittenWritten/formal. Says a decision has not yet been made; 「不定」 describes something inherently unfixed.
• Related曖昧あいまいNeutralNeutral. Covers vagueness and ambiguity, as in 「曖昧な返事」; 「不定」 is about being unfixed and apt to change.
• RelatedうやむやWrittenWritten/formal. Means leaving things hazy or letting them drop unresolved, as in 「うやむやにする」; 「不定」 is about being unfixed.
• RelatedあやふやCasualColloquial. Describes vague, unreliable memories or accounts, as in 「記憶があやふや」; 「不定」 is about being unfixed.
• Related不確かふたしかNeutralNeutral. Points to unreliability or lack of certainty, as in 「不確かな情報」; 「不定」 is about being unfixed.
• Related不明ふめいWrittenWritten/formal. Means unknown or unaccounted for, as in 「行方不明」; 「不定」 is about being unfixed.
• Related未解決みかいけつWrittenWritten/formal. Says a problem remains unsolved, as in 「未解決事件」; 「不定」 is about being unfixed.
• Related不確実ふかくじつWrittenWritten/formal. Says something is not certain or reliable, as in 「不確実性」; 「不定」 is about being unfixed.
• Related不明瞭ふめいりょうWrittenWritten/formal. Says pronunciation or explanations are unclear, as in 「発音が不明瞭」; 「不定」 is about being unfixed.
• Related宙ぶらりんちゅうぶらりんCasualColloquial. Evokes something hanging in midair or left in limbo, as in 「宙ぶらりんの状態」; 「不定」 is about being unfixed.
• Related曖昧模糊あいまいもこWrittenA written four-character compound for what is hazy and indistinct; 「不定」 stresses being unfixed and changeable.
• Related不分明ふぶんめいWrittenWritten/formal. Says something is unclear and hard to make out; 「不定」 is about being unfixed.
• Antonym一定いっていNeutralAntonym. Means fixed and unchanging, or a set amount, as in 「一定の速度」; the direct opposite of 「不定」.
• Antonym確定かくていWrittenWritten/formal antonym. Means clearly settled or finalized, as in 「判決確定」; the opposite of 「不定」.

Use 「不定」 for something not fixed and apt to change, as in 「住所不定」 or 「不定期」. For undecided matters pick 「未定」; for vagueness 「曖昧」; for unreliability 「不確か」; for something left hanging 「宙ぶらりん」. The written/formal terms — 「不確定」, 「未確定」, 「未決定」, 「不明」, 「未解決」 and others — each narrow the sense to their own context. The opposites are 「一定」 and 「確定」.

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

1. （ふてい）一定いっていしないこと。
2. （ふてい）方程式ほうていしきの解かいが無限むげんにあること。