Ru vs metallic element

Ru and metallic element both are nouns.

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

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

Ru: a rare polyvalent metallic element of the platinum group; it is found associated with platinum
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 Ru include metal.

Ru (noun)	metallic element (noun)
a rare polyvalent metallic element of the platinum group; it is found associated with platinum	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.