Green’s Dictionary of Slang

dead-set adv.

[dead set adj.]

(Aus.) definitely, certainly; also as excl.

[Aus]Bulletin (Sydney) 26 Apr. 44: Dead set the best bake in history they give me and I got the book for a shit pot dud.
[Aus]R. Aven-Bray Ridgey-Didge Oz Jack Lang 25: Dead Set Honestly!
[Aus]R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 19: This dead set shits on cartin’ beef.
[Aus]R.G. Barrett White Shoes 146: A bunch of wogs tried to kill me on Friday, Les. I’m dead-set lucky to be alive .
[Aus]Bug (Aus.) June [Internet] Dead set, it must be hard to be a Blues coach with so much talent.
[Aus]N. Cummins Tales of the Honey Badger [ebook] I was dead-set shitting myself.