In scholastic theology, a mode of duration with a beginning but no end. It is neither time (which measures change) nor eternity (which transcends change), but a third register attributed to angels and the blessed. Aeviternity names an endlessness that still remembers an origin.

From Medieval Latin aeviternitas, built on Latin aevum “age, aeon” (a long span, but not the absolute) and modeled against aeternitas “eternity.” The term belongs to the fine-grained metaphysics of time in the Middle Ages, where even the infinite had to be carefully qualified.