Merriam-Webster Collegiate Dictionary - inflexible

 adjective  Etymology: Middle English, from Latin inflexibilis, from in- + flexibilis flexible  Date: 14th century  1. rigidly firm in will or purpose ; unyielding  2. not readily bent ; lacking or deficient in suppleness  3. incapable of change ; unalterable  • inflexibility noun  • ~ness noun  • inflexibly adverb Synonyms:  ~, obdurate, adamant mean unwilling to alter a predetermined course or purpose. ~ implies rigid adherence or even slavish conformity to principle ~ in their demands. obdurate stresses hardness of heart and insensitivity to appeals for mercy or the influence of divine grace obdurate in his refusal to grant clemency. adamant implies utter immovability in the face of all temptation or entreaty adamant that the work should continue.  Synonym: see in addition stiff.