Tc vs metallic element

Tc and metallic element both are nouns.

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

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

Tc: a crystalline metallic element not found in nature; occurs as one of the fission products of uranium
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 Tc include metal.

Tc (noun)	metallic element (noun)
a crystalline metallic element not found in nature; occurs as one of the fission products of uranium	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.