INDOMITABLE

adj. resolute, resolved, determined, steadfast, staunch, persistent, unstoppable, irrepressible, indefatigable, untiring, tireless, unflagging, unyielding, unswerving, unwavering, unflinching, undaunted, dauntless, fearless, unafraid, intrepid, brave, courageous, plucky, mettlesome; unconquerable, unbeatable, invincible She survived the prison camp by dint of indomitable strength of character