Sb vs metallic element

Sb and metallic element both are nouns.

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

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

Sb: a metallic element having four allotropic forms; used in a wide variety of alloys; found in stibnite
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 Sb include metal.

Sb (noun)	metallic element (noun)
a metallic element having four allotropic forms; used in a wide variety of alloys; found in stibnite	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.