periodic vs occasional

periodic and occasional both are adjectives.

Word	Noun	Adjective	Verb	Adverb
periodic	No	Yes	No	No
occasional	No	Yes	No	No

As adjectives, periodic and occasional are synonyms defined as:

periodic (adjective)	occasional (adjective)
happening or recurring at regular intervals	occurring from time to time
recurring or reappearing from time to time	occurring on a temporary or irregular basis
	recurring or reappearing from time to time
	occurring or appearing at usually irregular intervals