1.  unalterable(a = adj.all) inalterable - not capable of being changed or altered; "unalterable resolve"; "an unalterable ground rule"
Antonym: alterable
Derived forms noun unalterability₂, noun unalterability₁

2.  unalterable(s = adj.all) - of a sentence; that cannot be changed; "an unalterable death sentence"

3.  unalterable(s = adj.all) changeless - remaining the same for indefinitely long times;
Derived forms noun unalterability₂, noun unalterability₁

unalterable, adj. not alterable.

Derivative:
unalterableness n. unalterably adv.

N  stability, immutability, unchangeability unchangeableness, constancy, stable equilibrium, immobility, soundness, vitality, stabiliment, stiffness, ankylosis, solidity, aplomb, establishment, fixture, rock, pillar, tower, foundation, leopard's spots, Ethiopia's skin, permanence, obstinacy, unchangeable, immutable, unaltered, unalterable, not to be changed, constant, permanent, invariable, undeviating, stable, durable, perennial, fixed, steadfast, firm, fast, steady, balanced, confirmed, valid, fiducial, immovable, irremovable, riveted, rooted, settled, established, vested, incontrovertible, stereotyped, indeclinable, tethered, anchored, moored, at anchor, on a rock, rock solid, firm as a rock, firmly seated, firmly established, deep-rooted, ineradicable, inveterate, obstinate, transfixed, stuck fast, aground, high and dry, stranded, stuck, jammed, unremovable, quiescent, deterioration, indefeasible, irretrievable, intransmutable, incommutable, irresoluble, irrevocable, irreversible, reverseless, inextinguishable, irreducible, indissoluble, indissolvable, indestructible, undying, imperishable, incorruptible, indelible, indeciduous, insusceptible, insusceptible of change, Int, stet, littera scripta manet.