happening, natural event, occurrence - an event that happens

migration - the periodic passage of groups of animals (especially birds or fishes) from one region to another for feeding or breeding

oscillation, cycle - a single complete execution of a periodically repeated phenomenon; "a year constitutes a cycle of the seasons"

repeat, repetition - an event that repeats; "the events today were a repeat of yesterday's"

sunrise - the daily event of the sun rising above the horizon

sunset - the daily event of the sun sinking below the horizon

heartbeat, beat, pulse, pulsation - the rhythmic contraction and expansion of the arteries with each beat of the heart; "he could feel the beat of her heart"

tide - the periodic rise and fall of the sea level under the gravitational pull of the moon