Silver is said to relate to the Moon, and with the human soul.  Silver is also associated with the dignity of kingship.  In legend, when the Irsh King Nuada lost his arm in battle and through the loss of a limb became disqualified from kingship, the god of healing, Dian Cecht, made him an artificial arm of silver, allowing him to return to the throne.  In many cultures, silver is the symbol of purity, and in Christian symbolism silver stands for divine wisdom.  Mystics assert that the soul is connected to the body by a silvery thread, which is sundered at death. 

Silver in European folklore has long been traditionally believed to be an antidote to various maladies and mythical monsters. Notably, silver was believed to be a repellent against vampires (this primarily originates from its holy connotations; also, mirrors were originally polished silver, and as such, vampires allegedly cannot be seen in them because they have no soul) and it was also believed that a werewolf, in his bestial form, could only be killed by a weapon or bullet made of silver. This has given rise to the term "silver bullet", which is used to describe things that very effectively deal with one specific problem.  Drugs such as salvarsan and penicillin, which were the first effective treatments for major diseases, are sometimes referred to as either "magic bullets" or "silver bullets."