Green’s Dictionary of Slang

a convict who has been transported to New South Wales, and subseq. escaped.

1848

‘Ned Buntline’ Mysteries and Miseries of N.Y. I 35: Nearly all of these fellows are ‘caffers’ – a slang term applied to the convicts of Botany Bay. [Ibid.] 113: ‘Caffers.’ Men who have been transported to Botany Bay from England, and have escaped.