The Collaborative International Dictionary of English v.0.48:

Inviolable \In*vi"o*la*ble\, a. [L. inviolabilis: cf. F.
   inviolable. See Inviolate, a.]
   [1913 Webster]
   1. Not violable; not susceptible of hurt, wound, or harm
      (used with respect to either physical or moral damage);
      not susceptible of being profaned or corrupted; sacred;
      holy; as, inviolable honor or chastity; an inviolable
      shrine.
      [1913 Webster]

            He tried a third, a tough, well-chosen spear,
            The inviolable body stood sincere.    --Dryden.
      [1913 Webster]

   2. Unviolated; uninjured; undefiled; uncorrupted.
      [1913 Webster]

            For thou, be sure, shalt give account
            To him who sent us, whose charge is to keep
            This place inviolable, and these from harm.
                                                  --Milton.
      [1913 Webster]

   3. Not capable of being broken or violated; as, an inviolable
      covenant, agreement, promise, or vow.
      [1913 Webster]

            Their almighty Maker first ordained
            And bound them with inviolable bands. --Spenser.
      [1913 Webster]

            And keep our faiths firm and inviolable. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inviolable
    adj 1: incapable of being transgressed or dishonored; "the
           person of the king is inviolable"; "an inviolable oath"
           [ant: violable]
    2: immune to attack; incapable of being tampered with; "an
       impregnable fortress"; "fortifications that made the frontier
       inviolable"; "a secure telephone connection" [syn:
       impregnable, inviolable, secure, strong,
       unassailable, unattackable]
    3: must be kept sacred [syn: inviolable, inviolate,
       sacrosanct]
    4: not capable of being violated or infringed; "infrangible
       human rights" [syn: absolute, infrangible, inviolable]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "inviolable":
   awesome, awful, blessed, chaste, consecrated, dependable, divine,
   faithworthy, hallowed, heavenly, holy, impenetrable, impregnable,
   incontestable, incorruptible, indomitable, ineffable, inenarrable,
   inexpressible, inexpugnable, insuperable, invincible, inviolate,
   invulnerable, irresistible, numinous, overpowering, overwhelming,
   proven, pure, reliable, religious, resistless, responsible, sacred,
   sacrosanct, spiritual, straight, sure, tested, to be trusted,
   tried, tried and true, true, trustable, trustworthy, trusty,
   unassailable, unbeatable, unconquerable, unfalse, unperfidious,
   unspeakable, unsubduable, unsurmountable, untouchable,
   untreacherous, unutterable, unyielding, venerable