Similar word to sempiternal:

abiding, ageless, always, amaranthine, boundless, ceaseless, constant, continual, continued, continuous, dateless, deathless, enduring, everlasting, forever, illimitable, immemorial, immortal, immutable, imperishable, incessant, indefinite, indestructible, infinite, interminable, lasting, never-ending, perdurable, perennial, permanent, perpetual, persistent, relentless, termless, timeless, unbroken, unceasing, undying, unending, unfading, uninterrupted, unremitting, without end