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]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]