The Collaborative International Dictionary of English v.0.48:

Irrecusable \Ir`re*cu"sa*ble\, a. [L. irrecusabilis; pref. ir--
   not + recusabilis that should be rejected, fr. recusare to
   reject: cf. F. irr['e]cusable.]
   Not liable to exception or rejection. --Sir W. Hamilton.
   [1913 Webster]