helium group vs series

helium group and series both are nouns.

Word	Noun	Adjective	Verb	Adverb
helium group	Yes	No	No	No
series	Yes	No	No	No

As nouns, series is a hypernym of helium group; that is, series is a word with a broader meaning than helium group:

helium group (noun)	series (noun)
the series of inert gases	(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