Englishimmutable
adjective
a precise and immutable set of rules:
unchangeable, fixed, set, rigid, inflexible, unyielding, unbending, permanent, entrenched, established, well established, unshakeable, irremovable, indelible, ineradicable;
unchanging, unchanged, changeless, unvarying, unvaried, undeviating, static, constant, lasting, abiding, enduring, persistent, perpetual.
▷antonyms variable.