Green’s Dictionary of Slang

fierce adv.

also fiercely

a general intensifier, whether positive or negative.

[[UK]Fielding Life of Jonathan Wild (1784) II 176: There were particularly two parties, viz. those who wore hats fiercely cocked, and those who preferred the Nab].
[UK]Reading Mercury 6 Apr. 4/5: A pair of tough cotton cord Kicksies, built quiet or fierce: Eight-and-twenty peg.
[US]W.J. Kountz Billy Baxter’s Letters 39: The band cut loose something fierce. The leader tore out about $9.00 worth of hair, and acted generally as though he had bats in his belfry.
[US]B. Fisher A. Mutt in Blackbeard Compilation (1977) 51: Mutt won a couple of million more in bughouse money yesterday. The odds he gets in the daffy joint are something fierce.
[US]‘Hugh McHugh’ You Should Worry cap. 8: Teddy talks slang something fierce.
[US]D.G. Rowse Doughboy Dope 45: And believe me, bo, they didn’t rub it into yuh. Fierce.
[UK]Wodehouse Carry on, Jeeves 177: Not what you would call a fiercely exciting spot.
[US]Z. Grey Sunset Pass 33: He razzed Ash somethin’ fierce.
[UK]P. Kavanagh Tarry Flynn (1965) 33: ‘Fierce great weather, Molly,’ said Tarry.
[US]H. Gold Man Who Was Not With It (1965) 239: We’re looking for a friend [...] You know him. Needed it bad, fierce.
[US]G.L. Coon Meanwhile, Back at the Front (1962) 110: God, the overhead around here is something fierce.
[US]C. Loken Come Monday Morning 113: You been fuckin’ up somethin’ fierce these las’ couple years.
[US]G.V. Higgins Cogan’s Trade (1975) 88: I played the dogs something fierce when I was in school.
[US]P. Benchley Lush 111: He can mess her up something fierce.
[Ire]J. O’Connor Salesman 279: What’ll they invent next? Somethin’ like that, I really would say that’s fierce handy, is it?