Inseparable

Part of speech: adjective (a.)

1. Not separable; incapable of being separated or disjoined. The history of every language is inseparable from that of the people by whom it is spoken. Mure. Liberty and union, now and forever, one and inseparable. D. Webster.

2. Invariably attached to some word, stem, or root; as, the inseparable particle un-.