adjective

unchanging over time or unable to be changed.

an immutable fact

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