[syn: ineffable, unnameable, unspeakable, unutterable]
The Collaborative International Dictionary of English v.0.48:
Ineffable \In*ef"fa*ble\, 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]
WordNet (r) 3.0 (2006):
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, ineffable,
           unspeakable, untellable, unutterable]
    2: too sacred to be uttered; "the ineffable name of the Deity"
       [syn: ineffable, unnameable, unspeakable,
       unutterable]
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