Synonyms and related words :
assiduous, beyond control, brave, breachy, constant, continuing, contumacious, courageous, dauntless, defiant, determined, diligent, dogged, enduring, faithful, fearless, fractious, immutable, impassable, impenetrable, impregnable, inalterable, incontestable, incorrigible, indefatigable, indocile, industrious, inexpugnable, insistent, insuperable, insuppressible, insurmountable, intractable, intrepid, invincible, inviolable, invulnerable, irrepressible, irresistible, lasting, loyal, mettlesome, never-tiring, obstinate, obstreperous, out of hand, overpowering, overwhelming, patient, patient as Job, permanent, perseverant, persevering, persistent, persisting, pertinacious, plodding, plucky, plugging, preoccupied, rapt, recalcitrant, refractory, relentless, resistant, resisting, resistless, resolute, resolved, restive, sedulous, shrewish, single-minded, sleepless, slogging, stable, staunch, steadfast, steady, stubborn, tenacious, tireless, unabating, unafraid, unassailable, unbeatable, unbiddable, unconquerable, uncontrollable, undaunted, undefeatable, undisciplined, undiscouraged, undrooping, unfailing, unfaltering, unflagging, unflinching, ungovernable, unintermitting, uninterrupted, unmalleable, unmanageable, unmoldable, unnodding, unrelaxing, unrelenting, unremitting, unruly, unsleeping, unstoppable, unsubduable, unsubmissive, unsurmountable, unswerving, untiring, unwavering, unwearied, unwearying, unwinking, unyielding, utterly attentive, weariless, wild