A billy club.
A good friend.
A billy goat.
A male goat; a ram.
A slubbing or roving machine.
A bong for smoking marijuana.
A tin with a swing handle used to boil tea over an open fire; a billycan; a billypot.
A condom.
A wooden (traditionally blackthorn (sloe) wood) club ending with a large knob.
Any cudgel, whether or not of Irish origin.