The Collaborative International Dictionary of English v.0.48:

Intenable \In*ten"a*ble\, a. [Pref. in- not + tenable: cf. F.
   intenable.]
   Incapable of being held; untenable; not defensible; as, an
   intenable opinion; an intenable fortress. [Obs.] --Bp.
   Warburton.
   [1913 Webster]