Green’s Dictionary of Slang

dead-ass adv.2

[dead adv. + -ass sfx]

(US) completely, wholly, utterly.

[US]J. Rechy City of Night 134: Im positively deadass tired.
[US]Playboy Dec. 338: He would rather be ‘dead-ass broke in New York than rich in MIssissippi’ [HDAS].
[US]C. Loken Come Monday Morning 144: Be a closet drinker? Lay out in your barn dead ass drunk two-three days atta time?
[US]R. Campbell In La-La Land We Trust (1999) 210: If they’d thought that Whistler’s sudden appearance was going to send Barcaloo into a dither, they were dead-ass wrong. He stared at Whistler like he was just another citizen waiting at a bus stop.
Alligator Online (FL) 3 Dec. [Internet] We begin the picks this week by bidding farewell to former columnist Andy ‘Shorn Scrotum’ Staples, who resigned this week because of intra-Alligator politics – not because he was on pace to finish dead-ass last in the Picks Column, or so he says.
Dict. Roadie Sl. [Internet] DAL – Dead-ass last, next best thing to DNF [did not finish].