rare earth vs grouping

rare earth and grouping both are nouns.

Word	Noun	Adjective	Verb	Adverb
rare earth	Yes	No	No	No
grouping	Yes	No	No	No

As nouns, grouping is a hypernym of rare earth; that is, grouping is a word with a broader meaning than rare earth:

rare earth: any element of the lanthanide series (atomic numbers 57 through 71)
grouping: any number of entities (members) considered as a unit

Other hypernyms of rare earth include group.

rare earth (noun)	grouping (noun)
any element of the lanthanide series (atomic numbers 57 through 71)	any number of entities (members) considered as a unit
	the activity of putting things together in groups
	a system for classifying things into groups