Pb vs metallic element

Pb and metallic element both are nouns.

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

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

Pb: a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey
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 Pb include metal, carbon group element, crystallogen, Group 14 element, tetragen, tetrel.

Pb (noun)	metallic element (noun)
a unit of information equal to 1000 terabits or 10^15 bits	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey