amalgam: an alloy of mercury with another metal (usually silver) used by dentists to fill cavities in teeth; except for iron and platinum all metals dissolve in mercury and chemists refer to the resulting mercury mixtures as amalgams
alloy: a mixture containing two or more metallic elements or metallic and nonmetallic elements usually fused together or dissolving into each other when molten
form: (biology) a group of organisms within a species that differ in trivial ways from similar groups