永久は英語で
eternity

英語の定義

永久
1. adj. eternal
2. n. permanence; continuing forever; being timeless; being eternally unchanging; eternity

eternity
1. n. Existence without end, infinite time.
2. n. (philosophy) Existence outside of time.
3. n. A period of time which extends infinitely far into the future.
4. n. (metaphysical) The remainder of time that elapses after death.
5. n. (informal, hyperbole) A comparatively long time.
It's been an eternity since we last saw each other.

permanence
1. 名詞. 永続性、不変

permanence
1. n. The state of being permanent.
2. n. (physics) The reciprocal of magnetic inductance.