Unyielding

determined firm fixed hard immovable inflexible relentless rigid single-minded staunch stiff stubborn tough unbending uncompromising unwavering adamant hardheaded headstrong mulish obdurate pertinacious pigheaded unrelenting hard-core hard-line hard-nosed implacable intractable merciless refractory ruthless solid stiff-necked uncompliant unmovable dead set on immalleable impliable inexorable locked in unswayable