Green’s Dictionary of Slang

(Aus.) a killer.

1885

Bulletin (Sydney) 23 May 18/3: He was a pigeon ‘scupperer,’ and as he made his way towards ‘Camperdown‘ for the great match he dropped into various pubs. for a ‘nerve steadier,’ but […] the more his nerves were steadied the worse his eye-sight grew, and when, at last, he stood facing the trap, he was a hopeless case – the string was pulled – the bird shot out, but still his gun was lowered.