Pb vs pig lead

Pb and pig lead both are nouns.

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

As nouns, pig lead is a hyponym of Pb; that is, pig lead is a word with a more specific, narrower meaning than Pb:

Pb: a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey
pig lead: lead that is cast in pigs

Other hyponyms of Pb include hard lead, antimonial lead, hard lead.

Pb (noun)	pig lead (noun)
a unit of information equal to 1000 terabits or 10^15 bits	lead that is cast in pigs
a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey