periodic event vs occurrent

periodic event and occurrent both are nouns.

Word	Noun	Adjective	Verb	Adverb
periodic event	Yes	No	No	No
occurrent	Yes	Yes	No	No

As nouns, occurrent is a hypernym of periodic event; that is, occurrent is a word with a broader meaning than periodic event:

Other hypernyms of periodic event include happening, natural event, occurrence.

periodic event (noun)	occurrent (noun)
an event that recurs at intervals	an event that happens

periodic event (adjective)	occurrent (adjective)
	presently occurring (either causally or incidentally)