the GNU version of the Collaborative International Dictionary of English
adj. Not decomposable; incapable or difficult of decomposition; not resolvable into its constituents or elements.
The Century Dictionary and Cyclopedia
Not decomposable; incapable of decomposition, or of being resolved into parts or elements.
Word Usage
"Such functionally indecomposable systems are extremely common…so common that the burden of proof rests on anyone who denies that such systems exist in the biological realm."