dateless, deathless, endless, eternal, everlasting, immortal, permanent, undying, unendingceaseless, continual, continued, continuing, continuous, incessant, nonstop, perpetual, running, unbroken, unceasing, uninterrupted, unremittingchangeless, constant, stable, steady, unchanging, unvaryingdurable, enduring, lasting, persistentimperishable, indestructible

intermittent, periodic, periodical, recurrent, recurringalternate, alternating, cyclic(or cyclical), rhythmic(or rhythmical), seasonal, serialerratic, fitful, irregular, occasional, spasmodic, sporadic, spotty, unsteadydiscontinuous, noncontinuous