Black Arrow
From Tolkien Gateway
When the dragon Smaug attacked Lake-town, after being disturbed by Thorin and Company in The Hobbit, the Black Arrow was the last of the arrows left in the quiver of Bard the Bowman.
According to Bard, this arrow had been passed down to him from his father and grandfather, and he believed it might have originated in the Lonely Mountain. He claimed that it had never failed him, and he had always been able to recover it.
It was this arrow that Bard fired through the vulnerable spot on Smaug's underbelly, described to him by the Thrush. The arrow penetrated the bare patch over Smaug's heart, killing the dragon immediately.
