happening, natural event, occurence, occurance, occurrance, nonoccurrence, reoccurrence, recurrence, incidence, occurring, more...

non-event, absence, nonexistence, inactivity, void

event, phenomenon, incident, episode, more...

frequent, common, rare, daily, unusual, actual, natural, uncommon, everyday, widespread, infrequent

what happens,   historical event,   an event,   historic event,   event happening,   entity phenomenon,   daily event,   ongoing event,   event in history,   one time event