Green’s Dictionary of Slang

1. (Aus.) a blow that comrehensively winds one’s opponent.

1857

Bell’s Life in Victoria (Melbourne) 24 Oct. 3/2: He fought on gamely in the hope of picking it [i.e. the fight] out of the fire by one of his favourite winders.

2. something so astounding that it ‘takes one’s breath away’.

1891

A. Day Mysterious Beggar 216: This old limb – oh, she’s a winder!’ Jip chuckled.