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永久
eikyū
eternity
この愛は永久に続くだろう。
This love will last forever.
formal
Eternity; permanence; perpetuity; immortality.
永久の平和を願う。
I pray for eternal peace.
永久に忘れない。
I will never forget.
Often used in abstract or philosophical contexts, such as love, peace, or memory. Can also describe physical objects intended to last indefinitely (e.g., 永久歯 'permanent teeth').
formal
Permanent; perpetual; everlasting.
永久凍土。
Permafrost.
Used as a na-adjective in compound nouns (e.g., 永久歯 'permanent teeth', 永久機関 'perpetual motion machine').
Related Phrases
Pro Tip
Distinguish from 永遠 (eien)
永遠 is more commonly used in everyday language to mean 'forever' or 'eternity' (e.g., 永遠に愛してる 'I will love you forever'). 永久 is more formal and often used in abstract, philosophical, or technical contexts.
Gold Rule
Use 永久 for permanence in a binding sense
In legal or technical documents, 永久 often implies a permanent, unchangeable state (e.g., 永久凍土 'permafrost', 永久歯 'permanent teeth').
Word Origin
From Middle Chinese 永久 (MC *ɦwiɐŋ|ɦjwɐŋX kuwX > Old Chinese *ɢʷraŋʔ kuʔ), meaning 'long time' + 'long duration'. The compound evolved in Japanese to mean 'eternity' or 'permanence'.
Usage Notes
永久 is more formal and philosophical than 永遠 (eternity). 永久 often implies something that is intended to last indefinitely, while 永遠 can refer to abstract concepts like time or love. In legal or technical contexts, 永久 may imply 'permanent' in a binding sense.
Word Breakdown
永
long (time)
root久
long (duration)
root和英辞典