Source : WordNet®

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