immitigable

from The Collaborative International Dictionary of English v.0.48

Immitigable \Im*mit"i*ga*ble\, a. [L. immitigabilis; fr. pref.
   im- not + mitigare to mitigate.]
   Not capable of being mitigated, softened, or appeased.
   --Coleridge.
   [1913 Webster]