from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A person; a fellow: That son of a gun knows how to sell cars and sell them well.
- n. A rascal; a scamp: That son of gun is always playing practical jokes.
- interj. Used to express annoyance, disappointment, or surprise.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. son of a bitch
The U.S. Navy publication Nomenclature of Ships (John Snelling, 1981) describes the origin of this phrase as follows: (Wiktionary)
The son of a gun lifts it twelve times, and a huge grin rushes across his beet-red face.