Despite my most concerted efforts, I have yet to find an acceptable etymology for this word. I can only surmise that it has been lost in the Mists Of Time.
Generic term for a cigarette in the Antipodeas, esp. Australia.
Short for 'Bull Durham' - an old brand of rolling tobacco.
"David Bradley, Australian Journal of Linguistics (1989) suggests that it may be derived from a widely used brand of loose tobacco used for roll-your-owns, Bull Durham, clipped and resuffixed with the most productive suffix for forming new colloquial words in Australian English."
Source: AUSTRALIAN NATIONAL DICTIONARY CENTRE