niobium vs metallic element

niobium and metallic element both are nouns.

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

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

niobium: a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium
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 niobium include metal.

niobium (noun)	metallic element (noun)
a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.