Green’s Dictionary of Slang

(Aus., Sydney) an impostor, a pretender, humbug; also as adj.

1852		G.C. Mundy Our Antipodes II 19: Bunyip became, and remains, a Sydney synonym for impostor, pretender, humbug, and the like.
1893		H. Lawson ‘The Darling River’ in Roderick (1972) 88: All the Darling bunyips are supposed to come from Adelaide.
1903		J. Furphy Such is Life 17: I got no patience with the ole bunyip. Can’t suffer fools, no road.
1938		X. Herbert Capricornia (1939) 357: What did I tell you about the Great Bunyip gettin’ us all down, eh?
1955		N. Pulliam I Travelled a Lonely Land (1957) 231/1: bunyip – a legendary animal, according to the abos. It has come to mean an impostor.
1993		K. Lette Foetal Attraction (1994) 122: That made her royalty at home. An antipodean Princess Di. Part of the bunyip aristocracy.
1999		G. Seal Lingo 16: (ref. to 1850s) At this time, in Sydney underworld parlance, ‘bunyip’ meant an imposter or con man.