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.
early 14c., "almighty, possessing infinite power," from Old French omnipotent "almighty, all-powerful" (11c.) and directly from Latin omnipotentem (nominative omnipotens) "all-powerful, almighty," from omnis "all" (see omni-) + potens (genitive potentis) "powerful" (see potent). Originally of God or a deity; general sense of "having absolute power or authority" is attested from 1590s. Related: Omnipotently.