Fun with synonyms - "eternity"

Question

What are the differences among the following two-kanji words that seem to mean "eternity":

• 永遠 {えいえん}
• 永久 {とわ}
• 永世 {えいせい}
• 永代 {えいたい}
• 永劫 {えいごう}
• 永永 {えいえい}
• 久遠 {きゅうえん}
• 悠久 {ゆうきゅう}
• 恒久 {こうきゅう}
• 恒常 {こうじょう}
• 長久 {ちょうきゅう}
• 無窮 {むきゅう}

Please include any other related words (preferably two-kanji only) but please exclude those that make use of period of a lifetime like 一生, 末代 etc, or big number of years/era like 千代, 万古 etc.

p/s: I noticed that the first two 永遠 and 永久 are the most commonly used; is it true and why them instead of the others?

Answer 1

There's a lot of good information in the other answer already, the main goal of this answer is to fill in some of the other definitions etc.

• 永遠{えいえん}:

  When something continues for all time in a certain state without ending, for example love which never ends or neverending world peace. 永遠に can take the meaning of "forever" or less commonly "permanently". Highly interchangeable with 永久{えいきゅう} and vice-versa.

• 永久{えいきゅう}:　

  Something which is permanent or perpetual, for example permanent love or a permanent license. Also used for immortal achievements, works, fame etc. 永久に can take the meaning of "permanently" or less commonly "forever".
  
  Usually えいきゅう, but can also be pronounced えいこう. Is sometimes pronounced とわ to take a more abstract meaning, but the Kanji 常{とわ} is more common with that reading according to Daijirin.

• 永世{えいせい}:

  A long period of months and years or an era which never ends. Also used in 永世[中立国]{ちゅうりつこく} as Joshua has noted.

• 永劫{えいごう}:

  An eon. (The other answer has already done a great job explaining about 永劫[回帰]{かいき} I think.)

• 永代{えいたい}:

  A very long time in months/years or eternity. Used in 永代[供養]{くよう}, "services performed in perpetuity by a Buddhist temple for the repose of a departed soul" according to JMDict.

• [永々]{えいえい}:

  I think this can mean "forever", but it generally just emphasizes a notably long period of time, e.g. "the practice has continued for 100 years." Usually written with a くりかえし (々) but can also be written as 永永.

• 久遠{くおん}:

  A buddhist term for eternity. Infinite time or the distant past/distant future. Usually pronounced くおん but can also be きゅうえん.

• 悠久{ゆうきゅう}:

  Unending. Used in 悠久の[歴史]{れきし} (neverending history.)

• 恒久{こうきゅう}:

  Used in permanent government/constitutions/laws/treaties/measures/solutions et al.

• 恒常{こうじょう}:

  Doesn't really mean "eternal" so much as "constant", e.g. "constant weather".

• 長久{ちょうきゅう}:

  Used in wars/battles to indicate eternal luck/good fortune e.g. [武運]{ぶうん}長久 and 幸運{こううん}長久. Also indicates the Choukyuu era from 10/11/1040-24/11/1044 as has been noted.

• 無窮{むきゅう}:

  Something which is always in a state which never changes, e.g. "an unchanging art style" or something which is of the state of being infinite/immortal.

Answer 2

1. 永遠{えいえん}

   [彼女]{かのじょ}は[夫]{おっと}を永遠に[愛]{あい}し[続]{つづ}けるであろう。
   I don't think she'll ever get sick of that guy (her husband).

2. 永久{えいきゅう}

   私はこの[出来事]{できごと}を永久に[忘]{わす}れない。
   I wont forget this.

3. 永世{えいせい}

   永世[中立国]{ちゅうりつこく}
   A Neutral Country (in Japanese without the word eisei it is not implied that a country has a policy of neutrality. Whereas, in English, the word Neutral Country by itself implies that this is a policy that the country has singed onto. The eisei portion of this word makes the idea a unchangeable bound policy.)

4. 永代{えいたい}

   pronounced eidai and this is used as a name of a person or place. There is a city in Tokyo called Eidai and a bridge called Eidai-bashi

5. 永劫{えいごう}

   永劫[回帰]{かいき}
   An ancient Greek philosophy called "Eternal Recurrence", which is also found in ideas like Reincarnation and the circle of life ideas, where life never dies, it just changes or revolves.

6. 永永{えいえい}

   永永[無窮]{むきゅう}の毎日
   "Same old same old" might be a good definition for the idea that there was nothing new that week and every day was kinda the same, unchanging.

7. 久遠{きゅうえん}

   Pronounced Ku-On and used in people's names

8. 悠久{ゆうきゅう}

   Sometimes written UQ and found in Game Titles but has the same meaning as Eien 永遠 except used for game or book or movie titles.

9. 恒久{こうきゅう}

   恒久的{こうきゅうてき}な平和など[幻想]{げんそう}に過ぎない。
   A world without war is a pipe dream. (in Japanese uninterrupted peace means a world without war)

10. 恒常{こうじょう}

    イングランドとスコットランドの間の[恒常的]{こうじょうてき}な[国境]{こっきょう}[戦争]{せんそう}は終わった。
    The constant border wars between England and Scotland finally came to an end.

11. 長久{ちょうきゅう}

    The name of the Japanese "Chokyu Era"

12. 無窮{むきゅう} (see number 6)

Answer 3

I'd like to add:　無限{むげん}. It means infinity but infinity and eternity can be interchangeable at times..