Bullet

a small metal projectile, part of a cartridge, for firing from small arms.
a cartridge.
a small ball.
Printing. a heavy dot for marking paragraphs or otherwise calling attention to or itemizing particular sections of text, especially in display advertising.
Cards. an ace.
to move swiftly.
bite the bullet, to force oneself to perform a painful, difficult task or to endure an unpleasant situation:
We’ll just have to bite the bullet and pay higher taxes.
Contemporary Examples

How a Rich Suburban Girl Became a Drug Kingpin Jeff Deeney July 9, 2009
Danger Stalks Lucas Davenport Daily Beast Promotions May 10, 2009
A Rage in Oakland Stanley Crouch January 8, 2009
Bridesmaids’ Gross-Out Girls Jennie Yabroff May 10, 2011
Gabrielle Giffords: What I Remember Mark Kelly October 7, 2012

Historical Examples

Surgical Experiences in South Africa, 1899-1900 George Henry Makins
Way of the Lawless Max Brand
Cardigan Robert W. Chambers
Way of the Lawless Max Brand
The Red Horizon Patrick MacGill

noun

a small metallic missile enclosed in a cartridge, used as the projectile of a gun, rifle, etc
the entire cartridge

something resembling a bullet, esp in shape or effect
(stock exchange) a fixed interest security with a single maturity date
(commerce) a security that offers a fixed interest and matures on a fixed date
(commerce)

the final repayment of a loan that repays the whole of the sum borrowed, as interim payments have been for interest only
(as modifier): a bullet loan

(Brit, slang) dismissal, sometimes without notice (esp in the phrases get or give the bullet)
(printing) See centred dot
bite the bullet, See bite (sense 14)
n.

An ace (1807+ Card games)
Money; dollars (1900+ Underworld)
A rivet (WWII aircraft workers)
Anything thrown or hit so as to travel very fast, esp a baseball: He’s throwing bullets out there (1940s+)
A record rising very fast on the popularity charts (1970s+ Recording industry)
A one-year prison sentence; boffo (1990s+ Police)

see:

bite the bullet
sweat bullets