bullet n.

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]