Green’s Dictionary of Slang

dead set adj.

[dead adv. + SE set, positioned]

1. fully committed.

J. Mitchell Nantucketisms 41: Dead set, determined.
[Aus]S. Maloney Big Ask 78: Naturally you’ll want to run the tape over us, see if we’re dead-set.
[Aus]L. Redhead Thrill City [ebook] She was deadset she was going to write the Great Australian Novel.

2. (Aus./US) superlative, in both positive and negative uses.

[US]J. Mitchell McSorley’s Wonderful Saloon (2001) 78: Personally, I’m a dead-set vegetarian.
[Aus]D. Ireland Glass Canoe (1982) 66: Ernie was a dead set prick — we all thought so.
[Aus]R.G. Barrett Real Thing 94: Les. You’ve done it again [...] You’re a dead-set genius.
[Aus]M.B. ‘Chopper’ Read How to Shoot Friends 131: Andy was a dead set menace.
[Aus]T. Winton Lockie Leonard, Legend (1998) 188: Vicki’s right. You’re a deadset legend.
[Aus]S. Maloney Sucked In 104: It was a dead-set certainty that we’d lose the next state election.
[Aus] F. McCarthy ‘Some Protection’ in Crime Factory: Hard Labour [ebook] Some of the most dead set crims, vicious, you’d ever want to keep away from.

In derivatives

dead-setter (n.)

a committed individual, irrespective of moral standpoint.

[UK]Illus. London News 17 Sept. 8/1: The man who looks you thro’ and thro’, / With, ’I’m as good a man as you’ — / A flash, bold, slang, dead-setter.

In phrases

dead set against (adj.)

totally hostile towards.

[US]Court Reports in Boston Morn. Post 31: Touching the court—the law, or what is worse, the judge, is dead set against the ‘nuisance’.
J.W. King Characters and Incidents 5: A good author has published a stupid book; everybody is dead set against it.
Forestry 3 146: What’s the use? Corn only thirty cents. Everything is dead set against the farmer.
[US]Deseret Wkly (UT) 5 July 63/3: The Free Church is dead set against their claims.
[UK]Sporting Times 18 Mar. 1/5: One of the best known publicans in Adelaide has, according to the ‘The Bulletin,’ long made a dead-set against barmaids.
[US]N.Y. Eve. Journal 7 Oct. in Fleming Unforgettable Season (1981) 297: Manager McGraw and Secretary Knowles are personally ‘dead set’ against giving [...] the Cubs a chance.
[US]Mansfield (OH) News 7 Dec. 10?/ 3: The Clean Language League of America, which is plum nuts about being dead set against slang, cuss words, risque stories, [etc.].
[UK]Burnley News 15 Aug. 2/4: The Football Association have always been dead-set against gambling.
[US]J.H. Burns Lucifer with a Book 88: Mr. Pilkey was dead set against division of the sexes at any faculty function.
[US]F. Kohner Gidget (2001) 23: He was dead set against the whole caboodle.
dead set on (adj.)

fascinated by, obsessed with, in love with, determined.

B. Taylor Story of Kennett 290: If he’'s dead-set on the wrong side, why, she ’s jist as dead-set on the right side.
[US]W.T. Call Josh Hayseed in N.Y. 34: I was dead sot [sic] on seein’ the court house.
[US]Cincinnati Commercial Gazette 17 Mar. 15/1: He is dead set on the club’s pulling down the Association pennant [DA].
[US]E. Townsend Chimmie Fadden Explains 41: Miss Fannie was dead set on havin all de folks bring dere kids and dere presents to our tree.
[US]Flynt & Walton Powers That Prey 119: If y’ ain’t dead set on bein’ sorry to part with her, y’ can git away from that door.
[Aus]Bulletin (Sydney) 27 July 32/1: More steam! I guess she’s drivin’ / Clean through the sloppy swells, / She’s that dead set on drivin’ / She thinks of nothin’ else.
[UK]Wodehouse Gentleman of Leisure Ch. ix: I want to marry one girl, and my uncle’s dead set on my marrying another.
[US]W.R. Burnett Iron Man 13: He ain’t dead set on winning from Mason, here.
[Ire](con. 1890s) S. O’Casey Pictures in the Hallway 8: But the O’Briens, the Dillons, and the Healeys [...] were dead set on making an end of him.
[UK]J. Maclaren-Ross Of Love And Hunger 10: He was dead-set on showing-off his wife to me.
[UK]‘Charles Raven’ Und. Nights 43: Peter [...] chummed up with another bloody-minded character, one Joe Tasker, who was also dead set on getting his discharge.