hard–and–fast

1 having been established and usually not subject to change hard-and-fast rules that governed the corporate environment in those days included strictures regarding office dress that were rigidly enforced Synonyms certain, determinate, final, firm, flat, frozen, hard, hard-and-fast, inexpugnable, set, settled, stableRelated Words nonadjustable, noncancelable, nonnegotiable, unchangeable; constant, steady, unchanging, uniform, unwavering; definite, exact, explicit, specific; given, stated, stipulated; dependable, good, reliable, responsible, safe, solid, sure, tried, tried-and-true, true, trustworthy, trustyNear Antonyms adjustable, changeable, negotiable; indefinite, open-ended, unspecified; capricious, changeful, flickery, fluctuating, fluid, inconstant, mercurial, mutable, temperamental, uncertain, unpredictable, unsettled, unstable, unsteady, variable, volatile

2 not capable of changing or being changed hard-and-fast beliefs that are the rock-solid foundation of their religion Synonyms fixed, hard-and-fast, immutable, inalterable, incommutable, invariable, unalterable, unchangeableRelated Words changeless, constant, determinate, established, set, settled, stable, steadfast, steady, unaltered, unchanging, unvarying; immovable, unmovableNear Antonyms adaptable, adjustable; fickle, fluctuating, inconstant, uncertain, unsettled, unstable, varying; plastic, pliable, pliant, supple, willowyAntonyms alterable, changeable, elastic, flexible, mutable, variable