Source : Webster's Revised Unabridged Dictionary (1913)

Indefinable \In`de*fin"a*ble\, a.
   Incapable of being defined or described; inexplicable. --Bp.
   Reynolds.

Source : WordNet®

indefinable
     adj 1: not capable of being precisely or readily described; not
            easily put into words; "an indefinable feeling of
            terror"; "an abstract concept that seems indefinable"
            [syn: {undefinable}]
     2: defying expression or description; "indefinable yearnings";
        "indescribable beauty"; "ineffable ecstasy";
        "inexpressible anguish"; "unspeakable happiness";
        "unutterable contempt"; "a thing of untellable splendor"
        [syn: {indescribable}, {ineffable}, {unspeakable}, {untellable},
         {unutterable}]