happening vs one-off

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, periodic event, 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.