Green’s Dictionary of Slang

a general intensifier, whether positive or negative.

[1743		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].
1829		Reading Mercury 6 Apr. 4/5: A pair of tough cotton cord Kicksies, built quiet or fierce: Eight-and-twenty peg.
1899		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.
1908		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.
1914		‘Hugh McHugh’ You Should Worry cap. 8: Teddy talks slang something fierce.
1918		D.G. Rowse Doughboy Dope 45: And believe me, bo, they didn’t rub it into yuh. Fierce.
1925		Wodehouse Carry on, Jeeves 177: Not what you would call a fiercely exciting spot.
1931		Z. Grey Sunset Pass 33: He razzed Ash somethin’ fierce.
1948		P. Kavanagh Tarry Flynn (1965) 33: ‘Fierce great weather, Molly,’ said Tarry.
1956		H. Gold Man Who Was Not With It (1965) 239: We’re looking for a friend [...] You know him. Needed it bad, fierce.
1961		G.L. Coon Meanwhile, Back at the Front (1962) 110: God, the overhead around here is something fierce.
1974		C. Loken Come Monday Morning 113: You been fuckin’ up somethin’ fierce these las’ couple years.
1974		G.V. Higgins Cogan’s Trade (1975) 88: I played the dogs something fierce when I was in school.
1989		P. Benchley Lush 111: He can mess her up something fierce.
1998		J. O’Connor Salesman 279: What’ll they invent next? Somethin’ like that, I really would say that’s fierce handy, is it?
2021		L. McInerney Rules of Revelation 66: ‘This is a fierce male city.’ ‘Fierce meaning violent?’ ‘Fierce meaning very’ [ibid.] 186: ‘Come down off that high horse fierce fast’.