Green’s Dictionary of Slang

1. a ball of dung on the buttocks of sheep or cattle.

1895

DN I. 387: Dingbat. Mr. Philip Hale, of the Boston Journal, has been collecting information . . . concerning this word. The following definitions appear: — (1) Balls of dung on buttocks of sheep or cattle.

2. (US) a cannon-ball, a bullet, a flying missile.

1877		Bartlett Dict. Americanisms (4th edn) 177: Dingbat [...] a cannonball; a bullet.
1895		DN I. 387: Dingbat. Mr. Philip Hale, of the Boston Journal, has been collecting information . . . concerning this word. The following definitions appear: — [...] (3) Flying missile.