Definition of eternal :
1. Continued without intermission; perpetual; ceaseless; constant.
2. Exceedingly great or bad; - used as a strong intensive.
3. Existing at all times without change; immutable.
4. One of the appellations of God.
5. That which is endless and immortal.
6. Without beginning or end of existence; always existing.
7. Without end of existence or duration; everlasting; endless; immortal.
thoroughgoing, ever-living, undying, indefinite, unremitting, deathless, unbroken, around-the-clock, gross, complete, eterne, unconquerable, temporary, without end, relentless, arrant, continuous, never-failing, stark, eonian, unending, ageless, unyielding, double-dyed, persistent, pure, aeonian, limited, sodding, unfailing, utter, nonstop, changeable, unfading, staring, forever, imperishable, inconstant, continue, indestructible, sempiternal, dateless, change, indomitable, consummate, round-the-clock, world without end, finite, fadeless, perfect, amaranthine, ongoing, unadulterated, always, never-ending
durable (part of speech: adjective)
perpetual (part of speech: adjective)
infinite (part of speech: adjective)
incalculable, unlimited, limitless, infinite, termless, everlasting, bottomless, innumerable, illimitable, boundless, interminable, countless, immeasurable, ceaseless, perpetual, timeless, unbounded, endless, numberless, inexhaustible, immemorial