periodical vs series

periodical and series both are nouns.

Word	Noun	Adjective	Verb	Adverb
periodical	Yes	Yes	No	No
series	Yes	No	No	No

As nouns, series is a hyponym of periodical; that is, series is a word with a more specific, narrower meaning than periodical:

Other hyponyms of periodical include digest, pictorial, serial, serial publication, organ, issue, number, journal, review.

periodical (noun)	series (noun)
a publication that appears at fixed intervals	(mathematics) the sum of a finite or infinite sequence of expressions
	a periodical that appears at scheduled times
	a serialized set of programs
	(sports) several contests played successively by the same teams
	similar things placed in order or happening one after another
	a group of postage stamps having a common theme or a group of coins or currency selected as a group for study or collection
	(electronics) connection of components in such a manner that current flows first through one and then through the other

periodical (adjective)	series (adjective)
happening or recurring at regular intervals