Synonyms and related words :
assiduous, beyond compare, beyond comparison, calculable, constant, continuing, deathless, dependable, diligent, dogged, easily first, enduring, facile princeps, faithful, faithworthy, fast, firm, immortal, immutable, impassable, impenetrable, imperishable, impregnable, inalterable, incomparable, incontestable, incorruptible, indefatigable, indelible, indestructible, indomitable, industrious, ineffaceable, ineradicable, inexpugnable, inextinguishable, inimitable, insistent, insuperable, insurmountable, inviolable, invulnerable, irresistible, lasting, loyal, matchless, never-tiring, nonperishable, nulli secundus, obstinate, overpowering, overwhelming, patient, patient as Job, peerless, permanent, perseverant, persevering, persistent, persisting, pertinacious, plodding, plugging, predictable, preoccupied, quenchless, rapt, relentless, reliable, resistless, resolute, second to none, secure, sedulous, single-minded, sleepless, slogging, solid, sound, stable, staunch, steadfast, steady, stubborn, substantial, sui generis, sure, surefire, tenacious, tireless, trustworthy, trusty, unabating, unapproachable, unapproached, unassailable, unattackable, unbeatable, unconquerable, undampable, undaunted, undefeatable, undefeated, undestroyable, undiscouraged, undrooping, undying, unequaled, unexampled, unexcelled, unfailing, unfaltering, unflagging, unflinching, unintermitting, uninterrupted, unique, unmatchable, unmatched, unnodding, unparagoned, unparalleled, unpeered, unquenchable, unrelaxing, unrelenting, unremitting, unrivaled, unsleeping, unstoppable, unsubduable, unsurmountable, unsurpassable, unsurpassed, unswerving, untiring, untouchable, unwavering, unwearied, unwearying, unwinking, unyielding, utterly attentive, weariless, well-founded, well-grounded, without equal, without parallel