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1.
Half Bat - Half Possum, a hybrid animal believed to exist in the Australian urban environment. The bossum has the build of a traditional possum (genus Cercartetus), with several key exceptions; bat like skin, short stumpy wings (for all intents and purposes useless) and a odd penchant for bitter ales.
Due to habitat reduction there has been reports of unprovoked bossum attacks on late night revelers. In short the bossum will fuck you up.
"Hey mate, did you see phil's scars from that bossum attack?"
by bossum hunter November 30, 2011
 
2.
Other word for boobs
Do you mind to show me your bossums?
by Doc Marco June 08, 2006
 
3.
a) When a boss does something awesome.

b) When somebody usually not a boss does something boss-like.
-That guy's a boss.

-Yeah, definitely. Everything he does is bossum.
by the Vocab Phantom March 24, 2010
 
4.
stuff that rules..!!..
that sick as drum solo was bossum..!
by McCheng April 11, 2006