antimonial lead vs Pb

antimonial lead and Pb both are nouns.

Word	Noun	Adjective	Verb	Adverb
antimonial lead	Yes	No	No	No
Pb	Yes	No	No	No

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

antimonial lead: a lead alloy that contains about 5% antimony
Pb: a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey

Other hypernyms of antimonial lead include atomic number 82, lead.

antimonial lead (noun)	Pb (noun)
a lead alloy that contains about 5% antimony	a unit of information equal to 1000 terabits or 10^15 bits
	a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey