noun

• A billy club.
• A billy goat.
• A male goat; a ram.
• (Tyneside) A good friend.
• (slang) A condom.
• A slubbing or roving machine.
• (UK, slang, obsolete) A silk handkerchief.
• (Australia, New Zealand) A tin with a swing handle used to boil tea over an open fire; a billycan; a billypot.
• (Australia, slang) A bong for smoking marijuana.
• A diminutive of the male given name William.
• (US, nickname) The B-25 twin-engine bomber aircraft used during World War Two, commonly called the "B-25 Mitchell" in honor of U.S. Army General William "Billy" Mitchell.