adamant, adamantine, adherent, adhesive, assiduous, balking, balky, bigoted, bulldogged, bulldoggish, bulldoggy, bulletheaded, bullheaded, cantankerous, cartilaginous, case-hardened, chewy, clingy, cohesive, constant, continuing, contumacious, coriaceous, determined, diligent, dogged, dogmatic, dour, durable, enduring, faithful, fanatic, fibrous, firm, fundamentalist, gluey, glutinous, gristly, gummy, hard, hardheaded, hardy, headstrong, hidebound, immovable, immutable, impliable, inalterable, indefatigable, indomitable, inductile, industrious, inelastic, inexorable, inextensible, inextensile, inextensional, inflexible, insistent, insubordinate, intolerant, intractable, intractile, intransigent, invincible, iron, ironbound, ironclad, ironhanded, irresilient, lasting, leatherlike, leathery, loyal, mulish, muscle-bound, never-tiring, nonelastic, nonstretchable, obdurate, obstinate, opinionated, ornery, orthodox, overzealous, patient, patient as Job, permanent, perseverant, persevering, persistent, persisting, pertinacious, pigheaded, plodding, plugging, preoccupied, procrustean, purist, puristic, puritan, puritanic, rapt, rebellious, recalcitrant, refractory, relentless, resistant, resolute, restive, rigid, rigorist, rigoristic, rigorous, rockbound, ropy, sedulous, self-adhesive, self-willed, set, sinewy, single-minded, sleepless, slogging, stable, steadfast, steady, stickable, sticky, stiff, stiff-necked, straightlaced, straitlaced, stringy, strong, strong-willed, strongheaded, stunt, sulky, sullen, tacky, tenacious, tireless, tough, tough as leather, unabating, unalterable, unbending, uncompromising, unconquerable, uncooperative, undaunted, undiscouraged, undrooping, unextendible, unextensible, unfailing, unfaltering, unflagging, unflexible, unflinching, ungiving, unintermitting, uninterrupted, unlimber, unmalleable, unnodding, unpliable, unpliant, unregenerate, unrelaxing, unrelenting, unremitting, unsleeping, unswerving, untiring, untractable, unwavering, unwearied, unwearying, unwinking, unyielding, utterly attentive, vigorous, viscid, wayward, weariless, willful, wiry