Source : Webster's Revised Unabridged Dictionary (1913)

Inexpiable \In*ex"pi*a*ble\, a. [L. inexpiabilis: cf. F.
   inexpiable. See {In-} not, and {Expiable}.]
   1. Admitting of no expiation, atonement, or satisfaction; as,
      an inexpiable crime or offense. --Pomfret.

   2. Incapable of being mollified or appeased; relentless;
      implacable. [Archaic] ``Inexpiable hate.'' --Milton.

            They are at inexpiable war with all establishments.
                                                  --Burke.

Source : WordNet®

inexpiable
     adj : incapable of being atoned for