What is the meaning of Billy?

A fellow, companion, comrade, mate; partner, brother.

A good friend.

A billy goat.

  1. (Can we verify this sense?) A male goat; a ram.

(Can we verify this sense?) A male goat; a ram.

A silk handkerchief.

A term applied to various machines or implements:

  1. A highwayman's club, billy club.
  2. A slubbing or roving machine.

A highwayman's club, billy club.

A slubbing or roving machine.

A tin with a swing handle used to boil tea over an open fire; a billycan; a billypot.

A bong for smoking marijuana.

A condom.

Source: wiktionary.org