indecomposable

from The Collaborative International Dictionary of English v.0.48

Indecomposable \In*de`com*pos"a*ble\, a. [Pref. in- not +
   decomposable: cf. F. ind['e]composable.]
   Not decomposable; incapable or difficult of decomposition;
   not resolvable into its constituents or elements.
   [1913 Webster]