inalterable

from WordNet (r) 3.0 (2006)

inalterable
    adj 1: not capable of being changed or altered; "unalterable
           resolve"; "an unalterable ground rule" [syn:
           {unalterable}, {inalterable}] [ant: {alterable}]

from The Collaborative International Dictionary of English v.0.48

Inalterable \In*al"ter*a*ble\, a. [Pref. in- not + alterable:
   cf. F. inalt['e]rable.]
   Not alterable; incapable of being altered or changed;
   unalterable. -- {In*al"ter*a*ble*ness}, n. --
   {In*al"ter*a*bly}, adv.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

72 Moby Thesaurus words for "inalterable":
      assiduous, constant, continuing, diligent, dogged, enduring,
      faithful, fixed, immovable, immutable, indefatigable, indomitable,
      industrious, insistent, invariable, invincible, lasting, loyal,
      never-tiring, obstinate, patient, patient as Job, permanent,
      perseverant, persevering, persistent, persisting, pertinacious,
      plodding, plugging, preoccupied, rapt, relentless, resolute,
      sedulous, single-minded, sleepless, slogging, stable, steadfast,
      steady, stubborn, tenacious, tireless, unabating, unalterable,
      unchangeable, unconquerable, undaunted, undiscouraged, undrooping,
      unfailing, unfaltering, unflagging, unflinching, unintermitting,
      uninterrupted, unmodifiable, unmovable, unnodding, unrelaxing,
      unrelenting, unremitting, unsleeping, unswerving, untiring,
      unwavering, unwearied, unwearying, unwinking, utterly attentive,
      weariless