Eternity

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late Middle English: from Old French eternite, from Latin aeternitas, from aeternus ‘without beginning or end’ (see eternal).

wiktionary

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From Middle English eternyte, from Old French eternité, eternitez, from Latin aeternitās.

etymonline

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eternity (n.)

late 14c., "quality of being eternal," from Old French eternité "eternity, perpetuity" (12c.), from Latin aeternitatem (nominative aeternitas), from aeternus "enduring, permanent," contraction of aeviternus "of great age," from aevum "age" (from PIE root *aiw- "vital force, life; long life, eternity"). Meaning "infinite time" is from 1580s. In the Mercian hymns, Latin aeternum is glossed by Old English ecnisse.