chronic

chronic adjective ceaseless, confirmed, constant, continual, continuing, continuous, cyclical, deep-rooted, deep-seated, drawn out, endless, enduring, entrenched, ever-present, everlasting, extended, forever, habitual, immedicable, incessant, inextinguished, lasting, lingering, long-lived, long-standing, longstanding, maintained, not averruncated, not restorable, of long duration, often, ongoing, perdurable, perennial, permanent, perpetual, persevering, persistent, persisting, prolonged, protracted, recurrent, recurring, regular, repeating, repetitive, resisting, returning, returning at intervals, serious, set, settled, steadfast, stubborn, sustained, unalleviated, unceasing, uncorrectable, undestroyed, undying, unending, unerasable, unfading, unhealable, uninterrupted, unmitigated, unmitigating, unremedied, unremittent, unremitting, unshifting, unslackening, unstopped, unsubsiding, unsuppressed, unvarying, unyielding, virulent, wearing

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See also: constant, durable, habitual, incorrigible, inveterate, permanent, perpetual, persistent, stable