Synonyms and related words :
ceaselessness, coeternity, constancy, continualness, continuance, durability, endlessness, eternalness, eternity, ever-duringness, everlastingness, everness, foreverness, immutability, incessancy, indestructibility, infinite duration, infinity, interminability, never-endingness, perdurability, perenniality, perennialness, permanence, perpetualness, perpetuity, sempiternity, stability, unceasingness