not flexible; incapable of or resistant to being bent; rigid: an inflexible steel rod.
of a rigid or unyielding temper, purpose, will, etc.; immovable: an inflexible determination.
not permitting change or variation; unalterable: inflexible rules.
Origin: 1350–1400;Middle English < Latininflexibilis rigid, unbending. See in-3, flexible
in·flex·i·bil·i·ty, in·flex·i·ble·ness, noun
Synonyms 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.
c.1400, "incapable of being bent, rigid," from L. inflexibilis, from inflexus, pp. of inflectere, from in- "not" + flectere "to bend." Figurative sense of "unbending in temper or purpose" first attested late 14c.