The Collaborative International Dictionary of English v.0.48:

Eternal \E*ter"nal\, n.
   1. One of the appellations of God.
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            Law whereby the Eternal himself doth work. --Hooker.
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   2. That which is endless and immortal. --Young.
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The Collaborative International Dictionary of English v.0.48:

Eternal \E*ter"nal\, a. [F. ['e]ternel, L. aeternalis, fr.
   aeternus. See Etern.]
   1. Without beginning or end of existence; always existing.
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            The eternal God is thy refuge.        --Deut.
                                                  xxxiii. 27.
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            To know wether there were any real being, whose
            duration has been eternal.            --Locke.
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   2. Without end of existence or duration; everlasting;
      endless; immortal.
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            That they may also obtain the salvation which is in
            Christ Jesus, with eternal glory.     --2 Tim. ii.
                                                  10.
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   3. Continued without intermission; perpetual; ceaseless;
      constant.
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            And fires eternal in thy temple shine. --Dryden.
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   4. Existing at all times without change; immutable.
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            Hobbes believed the eternal truths which he opposed.
                                                  --Dryden.
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            What are the eternal objects of poetry among all
            nations, and at all times?            --M. Arnold.
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   5. Exceedingly great or bad; -- used as a strong intensive.
      "Some eternal villain."
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   The Eternal City, an appellation of Rome.

   Syn: Everlasting; endless; infinite; ceaseless; perpetual;
        interminable. See Everlasting.
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WordNet (r) 3.0 (2006):

eternal
    adj 1: continuing forever or indefinitely; "the ageless themes
           of love and revenge"; "eternal truths"; "life
           everlasting"; "hell's perpetual fires"; "the unending
           bliss of heaven" [syn: ageless, aeonian, eonian,
           eternal, everlasting, perpetual, unending,
           unceasing]
    2: tiresomely long; seemingly without end; "endless debates";
       "an endless conversation"; "the wait seemed eternal";
       "eternal quarreling"; "an interminable sermon" [syn:
       endless, eternal, interminable]

Moby Thesaurus II by Grady Ward, 1.0:

123 Moby Thesaurus words for "eternal":
   ageless, all-comprehensive, all-inclusive, all-knowing,
   all-powerful, all-seeing, all-wise, almighty, boundless, ceaseless,
   changeless, coeternal, constant, continual, continuous, countless,
   creating, creative, dateless, deathless, endless, enduring,
   eternally the same, eterne, ever-being, ever-durable, ever-during,
   everlasting, everliving, exhaustless, extending everywhere, fixed,
   glorious, good, hallowed, highest, holy, illimitable, illimited,
   immeasurable, immemorial, immense, immortal, immutable,
   incalculable, incessant, incomprehensible, indestructible,
   inexhaustible, infinite, infinitely continuous, innumerable,
   interminable, interminate, invariable, just, lasting, limitless,
   loving, luminous, majestic, making, measureless, merciful,
   never-ceasing, never-ending, no end of, nonstop, nonterminating,
   nonterminous, numinous, olamic, omnipotent, omnipresent,
   omniscient, one, perdurable, permanent, perpetual, persistent,
   radiant, recurrent, relentless, sacred, sempiternal, shaping,
   shoreless, sovereign, steady, sumless, supreme, termless, timeless,
   ubiquitous, unalterable, unbounded, unceasing, unchanged,
   unchanging, uncircumscribed, undefined, undiminished, undying,
   unending, unfaltering, unfathomable, unintermitting, uninterrupted,
   universal, unlimited, unmeasurable, unmeasured, unnumbered,
   unplumbed, unremitting, untold, unvarying, unwavering,
   without bound, without end, without limit, without measure,
   without number