happening vs periodic event

Other hyponyms of happening include accompaniment, attendant, co-occurrence, concomitant, avalanche, experience, trouble, treat, miracle, marvel, wonder, thing, episode, contingence, contingency, eventuality, beginning, conclusion, ending, finish, one-off, recurrent event, alteration, change, modification, computer error, error, accident, chance event, fortuity, stroke, fire, incident, discharge, case, example, instance, motion, movement, failure, success, appearance, destiny, fate, disappearance, disappearance, contact, impinging, striking, finish, collapse, break, interruption, sound, union, news event, flash, convergence, juncture, occasion, burst, flare-up, outburst, eruption, irruption, outbreak, black eye, blow, reversal, reverse, setback, bonanza, boom, bunce, godsend, gold rush, gravy, manna from heaven, windfall, collapse, crash, supervention.