[1] : The Collaborative International Dictionary of English v.0.48

ineffable \inef"fable\, a. l. ineffabilis: cf. f. ineffable.
   see in- not, and effable, fame.
   incapable of being expressed in words; unspeakable;
   unutterable; indescribable; as, the ineffable joys of heaven.
   1913 webster

         contentment with our lot . . . will diffuse ineffable
         contentment over the soul.               --beattie.
   1913 webster
see also:
in- effable fame 

[2] : WordNet (r) 2.0

ineffable
     adj 1: defying expression or description; "indefinable yearnings";
            "indescribable beauty"; "ineffable ecstasy";
            "inexpressible anguish"; "unspeakable happiness";
            "unutterable contempt"; "a thing of untellable
            splendor" syn: indefinable, indescribable, unspeakable,
             untellable, unutterable
     2: too sacred to be uttered; "the ineffable name of the deity"
        syn: unnameable, unspeakable, unutterable
see also:
indefinable indescribable unspeakable untellable unutterable unnameable 

[3] : Moby Thesaurus II by Grady Ward, 1.0

53 moby thesaurus words for "ineffable":
   abstract, awesome, awful, celestial, divine, empyreal, empyrean,
   ethereal, exceptional, extraordinary, fabulous, heavenly, holy,
   ideal, incommunicable, indefinable, indescribable, inenarrable,
   inexpressible, innominable, inviolable, inviolate, legendary,
   marvelous, mythical, noncommunicable, noteworthy, numinous,
   phenomenal, portentous, prodigious, religious, remarkable, sacred,
   sacrosanct, spiritual, stupefying, stupendous, transcendent,
   transcendental, undefinable, unexampled, unmentionable, unnameable,
   unparalleled, unprecedented, unspeakable, untellable, untouchable,
   unutterable, unwhisperable, venerable, wonderful

Ineffable >> I Words
Ineffable, definition of term: Ineffable
ineffable_pag1.html