1.  gd(n = noun.substance) soman - a nerve agent easily absorbed into the body; a lethal cholinesterase inhibitor that is highly toxic when inhaled;
is a kind of organophosphate nerve agent

2.  gd(n = noun.substance) atomic number 64, gadolinium - a ductile silvery-white ductile ferromagnetic trivalent metallic element of the rare earth group;
is a kind of metal, metallic element

gd, symb. Chem. the element gadolinium.