1. unbendable, stiff. 2. rigorous, stern, unrelenting, unremitting, stubborn, obstinate, intractable, obdurate, unbending, adamant. Inflexible, relentless, implacable, inexorable imply having the quality of not being turned from a purpose. Inflexible means unbending, adhering undeviatingly to a set plan, purpose, or the like: inflexible in interpretation of rules; an inflexible will. Relentless suggests so pitiless and unremitting a pursuit of purpose as to convey a sense of inevitableness: as relentless as the passing of time. Implacable means incapable of being placated or appeased: implacable in wrath. Inexorable means unmoved by prayer or entreaty: inexorable in demanding payment. 3. undeviating.