I've come across a very good free combined dictionary and thesaurus (upgradable for a price of course) called WordWeb. It isn't web based as the name suggests. It downloads and runs from the computer. It can link to online dictionaries if desired. American and English dictionaries are supported. I wondered about Australian words too, so I typed in 'pom' and 'pommy'. The meanings were there (but without comprehensive description ).

Find it here (5.16Mb download)