Source : Webster's Revised Unabridged Dictionary (1913)

Inexterminable \In`ex*ter"mi*na*ble\, a. [L. inexterminabilis.
   See {In-} not, and {Exterminate}.]
   Incapable of extermination. --Rush.

Source : WordNet®

inexterminable
     adj : incapable of extermination or extirpation; "some weeds seem
           inextirpable" [syn: {inextirpable}]