silver bullet (n.)

"made of silver," late Old English seolfor, from the noun (see silver (n.), also compare silvern). Of voices, words, etc., from 1520s in reference to the metal's pleasing resonance; silver-tongued is from 1590s. Of hair by 1580s.

The silver age (1560s) was a phrase used by Greek and Roman poets. A silver fox is a North American variety of the common red fox with silver-tipped black hair.  A silver spoon in the literal sense is attested from late 15c.; see spoon (n.). The old figurative expression fish with a silver hook is attested from c. 1600.

The Silver Hook, and the Golden Bait, catch all the Fish upon dry Land. [Defoe, "The Union-Proverb," 1708]

1550s, "cannonball" (a sense now obsolete), from French boulette "cannonball, small ball," diminutive of boule "a ball" (13c.), from Latin bulla "round thing, knob" (see bull (n.2)). The meaning "small ball," specifically a metal projectile meant to be discharged from a firearm, is from 1570s. Earliest version of the figurative phrase bite the bullet "do something difficult or unpleasant after delay or hesitation" is from 1891, probably with a sense of giving someone a soft lead bullet to clench in the teeth during a painful operation.

Beggars' bullets—stones thrown by a mob, who then get fired upon, as matter of course. [John Bee, "Slang," 1823]