erbium vs metallic element

erbium and metallic element both are nouns.

Word	Noun	Adjective	Verb	Adverb
erbium	Yes	No	No	No
metallic element	Yes	No	No	No

As nouns, metallic element is a hypernym of erbium; that is, metallic element is a word with a broader meaning than erbium:

erbium: a trivalent metallic element of the rare earth group; occurs with yttrium
metallic element: any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.

Other hypernyms of erbium include metal.

erbium (noun)	metallic element (noun)
a trivalent metallic element of the rare earth group; occurs with yttrium	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.