Source : Webster's Revised Unabridged Dictionary (1913)

Insupportable \In`sup*port"a*ble\, a. [L. insupportabilis: cf.
   F. insupportable. See {In-} not, and {Support}.]
   Incapable of being supported or borne; unendurable;
   insufferable; intolerable; as, insupportable burdens;
   insupportable pain. -- {In`sup*port"a*ble*ness}, n. --
   {In`sup*port"a*bly}, adv.

Source : WordNet®

insupportable
     adj : incapable of being justified or explained [syn: {indefensible},
            {unjustifiable}, {unwarrantable}, {unwarranted}]