Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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