billy, n.⁷ — Green’s Dictionary of Slang

billy n.⁷

[play on SAusE billy, a form of kettle]

(Aus. drugs) a form of pipe used for smoking cannabis; thus a puff on such a pipe.

1994		Ad News 28 Jan. 19: Billy – Vessel for marijuana consumption.
2012		‘First Dog on the Moon’ in crikey,com.au 2 July 🌐 There were like 15 bongs [...] And people were all ‘Emily, have a billy’.