Green’s Dictionary of Slang

(Aus./N.Z.) a wet suit.

1985		Tracks (Aus.) Dec. 20: Putting on my wettie, I picked up my board and jogged towards the water [Moore 1993].
1993		T. Winton Lockie Leonard: Scumbuster (1995) 163: ‘Get on board, Phillip.’ ‘I’ll get the wetty.’.
2004		T. Winton ‘Family’ in Turning (2005) 174: He didn’t know if it was the cold or fatigue or simple nerves that caused him to shake so much but he had trouble getting the wetty on.