inseparable

from WordNet (r) 3.0 (2006)

inseparable
    adj 1: not capable of being separated; "inseparable pieces of
           rock"

from The Collaborative International Dictionary of English v.0.48

Inseparable \In*sep"a*ra*ble\, a. [L. inseparabilis: cf. F.
   ins['e]parable. See {In-}, and {Separable}.]
   [1913 Webster]
   1. Not separable; incapable of being separated or disjoined.
      [1913 Webster]

            The history of every language is inseparable from
            that of the people by whom it is spoken. --Mure.
      [1913 Webster]

            Liberty and union, now and forever, one and
            inseparable.                          --D. Webster.
      [1913 Webster]

   2. (Gram.) Invariably attached to some word, stem, or root;
      as, the inseparable particle un-.
      [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

23 Moby Thesaurus words for "inseparable":
      bound up in, bound up with, close, coherent, cohesive, familiar,
      hand and glove, hand-in-hand, impartible, inalienable,
      indiscerptible, indissoluble, indissolvable, indivisible,
      infrangible, infusible, insoluble, intimate, near, thick,
      thick as thieves, undividable, unified