Cd vs metallic element

Cd and metallic element both are nouns.

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

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

Cd: a soft bluish-white ductile malleable toxic bivalent metallic element; occurs in association with zinc ores
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 Cd include metal.

Cd (noun)	metallic element (noun)
a soft bluish-white ductile malleable toxic bivalent metallic element; occurs in association with zinc ores	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.