Green’s Dictionary of Slang

(Aus.) anything notable, amazing etc; also as adj.

1941		Baker N.Z. Sl.
1964		‘Hori’ Fill It Up Again 63: At last [I] bring in a whopcacker stingray [DNZE].
1966		G.W. Turner Eng. Lang. in Aus. and N.Z. 121: Woopcacker seems to apply to things as well as people. The word illustrates the lack of standardization in these seldom written words: I would have spelt it wopcacker. Baker records the word as whopcacker but gives a slightly variant meaning, as ‘very good’ [DNZE].
1969		B. Mason Awatea (1978) 37: Will you just look at this dirty big wop-kacker! [Ibid.] 98: wop-kacker: New Zealand slang for ‘thingummy’, implying size, proportion, remarkable qualities. Etymology dubious.
1972		Dominion (Wellington) 17 June 26: I’ve been trying to find space for my notes on a ‘Glossy’ subtitled ‘This Will Really Kill You’. It’s a wopcacker if ever there was, so here goes [DNZE].
1988		McGill Dict. of Kiwi Sl. 123/1: whopcacker extravagantly approved person or thing; extension probably of ‘whop’ or ‘wop’, to excel.
1993		O. Marshall ‘The Bank Section’ in Ace of Diamonds Gang 122: Yea, well remember the size of some of them. Bloody wopcackers.
2003		McGill Reed Dict. of N.Z. Sl. 231: whopcacker/wopcacker Outstanding person or thing, perhaps evolved from a ‘whopper’ or large lie. ANZ 1920s.