Waiali, Wali : Brushtail Possum in the Darug dialect (local to the Sydney area) found on http://www.thehills.nsw.gov.au/IgnitionSuite/uploads/docs/Traditional%20Aboriginal%20Names%20BH%20Shire(1).pdf
There are slightly different versions of how the 'possum got its name. From WikiPedia (see also link below): The Virginia Opossum is the original animal named "opossum". The word comes from...