See persistent in Webster's New World Roget's A-Z Thesaurus II
adjective
Firm or obstinate, as in making a demand or maintaining a stand:
importunate, importune, insistent, urgent. See continueExisting or occurring without interruption or end:
around-the-clock, ceaseless, constant, continual, continuous, endless, eternal, everlasting, incessant, interminable, nonstop, ongoing, perpetual, relentless, round-the-clock, timeless, unceasing, unending, unfailing, uninterrupted, unremitting. See continueExisting or remaining in the same state for an indefinitely long time:
abiding, continuing, durable, enduring, lasting, long-lasting, long-lived, long-standing, old, perdurable, perennial, permanent. See continueOf long duration:
chronic, continuing, lingering, prolonged, protracted. See continueDifficult to alleviate or cure:
obstinate, pertinacious, stubborn. See continue
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