The Collaborative International Dictionary of English v.0.48:

Insusceptible \In`sus*cep`ti*ble\, a. [Pref. in- not +
   susceptible: cf. F. insusceptible.]
   Not susceptible; not capable of being moved, affected, or
   impressed; that can not feel, receive, or admit; as, a limb
   insusceptible of pain; a heart insusceptible of pity; a mind
   insusceptible to flattery; new strains of bacteria
   insusceptible to penicillin. -- In`sus*cep`ti*bly adv.
   [1913 Webster]