1. (a.) Firm; stiff; unyielding; not pliant; not flexible.

2. (a.) Hence, not lax or indulgent; severe; inflexible; strict; as, a rigid father or master; rigid discipline; rigid criticism; a rigid sentence.

abiding accurate adamant adamantine at a standstill attentive austere buckram careful cast-iron changeless close conscientious constant continuing correct critical delicate demanding detailed determined direct dogged dour draconian durable enduring even exact exacting exigent express exquisite faithful fine finical finicking finicky firm firm as Gibraltar fixed flinty frozen fundamentalist fussy grim hard hard and fast hard-core hard-line harsh headstrong hidebound immobile immotile immotive immovable immutable implacable impliable in buckram inelastic inerrable inerrant inexorable infallible inflexible infrangible intact intransigent inviolate iron ironbound ironclad ironhanded irreconcilable irremovable lasting literal made of iron mathematical meticulous micrometrically precise microscopic minute mulish muscle-bound narrow nice obdurate obstinate orthodox painstaking particular pat permanent perpetual persevering persistent pigheaded pinpoint pokerlike precise precisianistic precisionistic prim procrustean punctilious punctual purist puristic puritan puritanic quiescent ramrodlike refined relentless religious religiously exact remaining renitent resolute resolved rigorist rigoristic rigorous rock-ribbed rockbound rodlike scientific scientifically exact scrupulous scrutinizing set severe single-minded solid sound square stable standpat starch starched starchy static stationary staunch staying steadfast steely stern stiff stiff as buckram stilted stout straightlaced strait-laced straitlaced strict stringent strong stubborn sturdy subtle sustained taut tenacious tense thorough tight torpid tough unadaptable unaffected unalterable unaltered unbending unbreakable unchangeable unchanged unchanging unchecked uncompliant uncompromising undestroyed undeviating unerring unfading unfailing unflexible ungiving unmovable unmoved unmoving unqualified unrelaxed unrelenting unshifting unswerving unvaried unvarying unwavering unyielding virgate