The Collaborative International Dictionary of English v.0.48:

Indestructible \In`de*struc"ti*ble\, a. [Pref. in- not +
   destructible: cf. F. indestructible.]
   Not destructible; incapable of decomposition or of being
   destroyed; as, the Russian harvesters had primitive
   electronics, but they were built so sturdily they were almost
   indestructible. -- In`de*struc"ti*ble*ness, n. --
   In`de*struc"ti*bly, adv.
   [1913 Webster]