pertinacious

pertinacious adjective adamant, adhering to a purrose, assidous, bent, bullheaded, certain, continuing, determined, diligent, dogged, earnest, enduring, exhibiting purpose, faithful, firm, hard to get rid of, holding to a purpose, immovable, immutable, indefatigable, indomitable, industrious, inflexible, insistent, intent, intractable, inveterate, mulish, obdurate, obstinate, obstinatus, painstaking, patient, persevering, persistent, persisting, pertinax, pervicacious, pervicax, pigheaded, plodding, purposeful, relentless, resolute, resolved, rigid, sedulous, self-willed, serious, set, single-minded, stalwart, stanch, steadfast, steady, strong-willed, stubborn, sure, tough, unbending, uncompromising, undaunted, undoubting, unfaltering, unflagging, unmovable, unrelaxing, unrelenting, unremitting, unshakable, unshaken, unshrinking, unswerving, untiring, unwavering, unwearying, unyielding, willful, zealous

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See also: diligent, faithful, inexorable, inflexible, insistent, intractable, obdurate, patient, persistent, relentless, resolute, sedulous, steadfast, unrelenting, unremitting, unyielding