Inseparable, a.
Etymology: [L. inseparabilis: cf. F. inséparable. See In-, and Separable.]
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. (Gram.)
Invariably attached to some word, stem, or root; as, the inseparable particle un-.
Shades of meaning
Fernald has no entry of its own for inseparable; he lists it under inherent.
Where he writes about it:
That which is inherent is an inseparable part of that in which it inheres, and is usually thought of with reference to some outworking or effect; as, an inherent difficulty. — from inherent