恒久|こうきゅうkoukyuu[0]heiban (flat)

1. no-adjectivepermanence; perpetuity

• Synonym永遠えいえんNeutralThe everyday word for eternity, often with emotional color as in 「永遠の愛」; 「恒久」 belongs to written prose, describing a state that lasts unchanged, and is seldom lyrical.
• Synonym永久えいきゅうNeutralClosest to 「恒久」 in meaning and at home in both speech and writing, as in 「永久保存」「永久歯」; 「恒久」 is the more written choice and typically appears as 「恒久的」.
• Synonym悠久ゆうきゅうWrittenWritten word mostly for history or nature stretching down from long ago, as in 「悠久の歴史」; 「恒久」 looks instead at something staying unchanged over a long time.
• Synonym永世えいせいWrittenWritten word for eternity and successive generations, as in 「永世中立」, also lifetime titles in shogi or go; 「恒久」 is never used as a title.
• Synonym永代えいたいWrittenWritten word confined largely to set religious and property phrases like 「永代供養」「永代使用」; 「恒久」 applies broadly to anything lasting unchanged.
• Synonym長久ちょうきゅうWrittenWritten word for long continuance, seen in felicitations like 「武運長久」, and also a former era name; 「恒久」 stresses remaining unchanged and works as 「恒久的」.
• Synonym永劫えいごうWrittenWritten word with a Buddhist tinge for an immensely long span of time, familiar from 「未来永劫」; 「恒久」 also means long duration but stresses a state staying unchanged.
• Synonym久遠くおんWrittenElegant written word that can point to the distant past or future, as in 「久遠の昔」; 「恒久」 never refers to the past, only to remaining unchanged from here on.
• Synonym無窮むきゅうWrittenWritten word for endlessness in both time and space, as in 「天壌無窮」; 「恒久」 concerns time alone — lasting unchanged — and has no spatial sense.
• Related千代ちよWrittenElegant word for a thousand years or long ages, heard in waka and blessings like 「千代に八千代に」; for lasting unchanged in daily language use 「恒久」 or 「永久」.
• Related万世ばんせいWrittenThe same word in its variant form 「万世」: an archaic, laudatory term for generation after generation; modern prose says lasting permanence with 「恒久」 or 「永久」.
• Related万代ばんだいWrittenArchaic and elegant, meaning endless generations down the ages, much used in congratulations; 「恒久」 is ordinary written prose for a thing lasting unchanged.
• Related生々世々しょうじょうせぜWrittenBuddhist term for life after life through the cycle of rebirth, also adverbial for forever; rare in modern prose, where 「永遠」 is the normal choice.
• Related永久とわNeutralClosest to 「恒久」 in meaning and at home in both speech and writing, as in 「永久保存」「永久歯」; 「恒久」 is the more written choice and typically appears as 「恒久的」.
• Related常世とこよWrittenArchaic word that, besides eternal unchangingness, names a land over the sea or the world of the dead, as in 「常世の国」; today 「恒久」 covers the lasting sense.
• Related千古せんこWrittenWritten word covering both remote antiquity and eternity, as in 「千古の昔」「千古不易」; 「恒久」 has no sense of antiquity, only of lasting unchanged.
• Related万古ばんこWrittenWritten word usually for the remote past onward, as in 「万古不易」; 「恒久」 carries no antiquity sense, pointing only to unchanging continuance.
• Related万劫ばんごうWrittenBuddhist term for the vast span of countless kalpas, now rarely seen; ordinary writing says lasting unchanged with 「恒久」 or 「永遠」.
• Related未来永劫みらいえいごうWrittenFour-character written phrase, mostly adverbial for strong emphasis, as in 「未来永劫許さない」; far more emphatic and hyperbolic than 「恒久」.
• RelatedエタニティNeutralLoanword seen mostly in product and work titles, as in 「エタニティリング」; ordinary prose says 「永遠」, and it does not stand in for 「恒久」.
• Related万劫末代まんごうまつだいWrittenFour-character written word for forever and countless generations, now rare and hyperbolic; ordinary prose gets by with 「永遠」 or 「恒久」.
• AntonymひとときNeutralA short while or moment, as in 「楽しいひと時」; the opposite of 「恒久」 in how long something lasts.
• Antonym短期たんきNeutralShort-term, as in 「短期留学」「短期的」; opposite of 「恒久」 in length of term, though the usual opposite of 「恒久的」 is 「一時的」.

「恒久」 is a written-style word for something lasting unchanged, typically as 「恒久的」, as in 「恒久平和」 and 「恒久的な価値」. For everyday talk of forever, 「永遠」 is the common choice and 「永久」 the closest match, fine in both speech and writing. For history stretching far back, use 「悠久」. The remaining literary words — 永劫, 久遠, 万代, 千代 and the like — are elegant, archaic or Buddhist set expressions, mostly in fixed phrases. Opposites: 「短期」 and 「ひと時」.

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

1. ずっと変かわらないこと。また、事案じあんが確定かくていして、長ながい期間きかんを前提ぜんていにしていること。