unalterable

from WordNet (r) 3.0 (2006)

unalterable
    adj 1: not capable of being changed or altered; "unalterable
           resolve"; "an unalterable ground rule" [syn:
           {unalterable}, {inalterable}] [ant: {alterable}]
    2: of a sentence; that cannot be changed; "an unalterable death
       sentence"
    3: remaining the same for indefinitely long times [syn:
       {changeless}, {unalterable}]

from Moby Thesaurus II by Grady Ward, 1.0

86 Moby Thesaurus words for "unalterable":
      adamant, adamantine, cast-iron, changeless, constant, dour, firm,
      fixed, flinty, grim, hard, hard-core, immovable, immutable,
      implacable, impliable, inalterable, incommutable, inconvertible,
      indefeasible, inductile, inelastic, inert, inexorable,
      inextensible, inextensile, inextensional, inflexible,
      insusceptible of change, intractable, intractile, intransigent,
      intransmutable, invariable, iron, irreconcilable, irresilient,
      irretrievable, irreversible, irrevocable, lasting, noble,
      nonelastic, nonreturnable, nonreversible, nonstretchable,
      permanent, relentless, reverseless, rigid, rigorous, rock-ribbed,
      steely, stern, stiff, stubborn, unaffected, unalterative,
      unaltered, unbending, unchangeable, unchanged, unchanging,
      uncompromising, undeflectable, undeviating, unextendible,
      unextensible, unflexible, ungiving, unlimber, unmalleable,
      unmodifiable, unmovable, unmoved, unpliable, unpliant, unrelenting,
      unremitting, unrestorable, unreturnable, unsusceptible,
      untractable, unvariable, unvarying, unyielding