How to say "eternally" in Japanese

• いつまでもJLPT N3approx.Common
  adverbThe common everyday adverb for 'forever' or 'eternally,' also covering 'for good' and doing something 'as long as one likes'; normally written in kana alone, it is the default choice.
  私はいつまでも彼かれの名なを覚おぼえている。↗

  I still bear his name in mind.
• 果てし無くはてしなく
  adverbEmphasizes sheer endlessness — something going on and on with no end in sight; with its 'interminably' sense it can suggest weariness at the length, so it suits endless stretches rather than timeless permanence.
• 尽未来じんみらい
  nounA Buddhist-derived term meaning 'to the very end of the future'; because of its religious coloring it is seldom the everyday word for 'eternally,' appearing mainly in Buddhist and literary language.
• 常住じょうじゅう
  adverbTreats 'eternally' as a state rather than a duration: the permanence or eternal, unchanging existence of something, a term rooted in Buddhist doctrine, not the ordinary adverb for 'forever.'
• 幾久しくいくひさしく
  adverbA literary adverb wishing that something last forever; it is especially at home in formal written closings wishing someone lasting health or prosperity, so it is not the neutral word for 'eternally.'

Use 「いつまでも」 for everyday 'forever' or 'eternally' (also 'for good' and 'as long as one likes'); 「果てし無く」 stresses endlessness or tedium; 尽未来 and 常住 are Buddhist terms; 「幾久しく」 suits formal written wishes.

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

• いつまでもforever
• 果てし無くはてしなくeternally
• 尽未来じんみらいeternally
• 常住じょうじゅうalways
• 幾久しくいくひさしくforever
• 末代までまつだいまでforever