inseparable

Etymology

From Middle English, from Middle French inséparable, from Latin īnsēparābilis. Constructed as in- + separable.

adj

1. Unable to be separated; bound together permanently.
   =This detail is one of the reasons which made a single, modern signalbox and the marshalling yard inseparable features in the modernisation of the Perth facilities. A central control point rather than 13 individual boxes, was essential to integrate with other movements the greatly increased flow of freight traffic through the station area. 1962 October, G. Freeman Allen, “The New Look in Scotland's Northern Division—II”, in Modern Railways, page 271

noun

1. Something that cannot be separated from something else.
   Jayanta does so in answering an opponent who declares that the very idea of a relation between two inseparables is self-contradictory. How can inseparability and relation be reconciled? 2002, Brian Carr, Indira Mahalingam, Companion Encyclopedia of Asian Philosophy, page 129