The Collaborative International Dictionary of English v.0.48:

Insentient \In*sen"ti*ent\, a.
   Not sentient; not having perception, or the power of
   perception; devoid of feeling, consciousness and animation;
   inanimate; as, insentient stone. Opposite of sentient.
   [WordNet sense 1+3]

   Syn: inanimate, insensate.
        [1913 Webster + WordNet 1.5]

              The . . . attributes of an insentient, inert
              substance.                          --Reid.
        [1913 Webster]

              But there can be nothing like to this sensation in
              the rose, because it is insentient. --Sir W.
                                                  Hamilton.
        [1913 Webster]

   2. incapable of sensation.

   Syn: insensate, insensible.
        [WordNet 1.5]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "insentient":
   abiotic, asleep, azoic, benumbed, callous, dead, deadened, dull,
   dumb, exanimate, impassible, impassive, imperceptive, impercipient,
   inanimate, inanimated, inert, insensate, insensible, insensitive,
   lifeless, mute, nonconscious, nonliving, numb, numbed, obdurate,
   obtuse, senseless, soulless, thick-skinned, thick-witted,
   unanimated, unconscious, unfeeling, unfelt, unimpressible,
   unimpressionable, unperceptive, unresponsive, unsusceptible