Green’s Dictionary of Slang

(US) Broadway, New York City, in the area immediately around Times Square, spec. 40th Street to 49th Street.

1908		Eve. Star (DC) 20 Dec. 31/3: It was [...] there in ‘the roaring forties’ when they first met [...] and elected young Billy Ross as their president.
1910		News Herald (Hillsboro, OH) 3 Nov. 6/1: Turning west toward the bacheolor rooms which Kellog had established in he roaring forties just the other side of [...] Fifth avenue.
1919		Bisbee Dly Rev. (AZ) 1 Jan. 5/2: The oldest inhabitants of Broadway and adjacent streets in the ‘roaring forties’ admitted [...] it was the most successful New Year’s eve they could remember.
1922–24		O.O. McIntyre White Light Nights 86: Over in the Roaring Forties workmen were fashioning a new supper club.
1924		T. Thursday ‘A Lodging for the Knight’ in Top-Notch Mag. 1 Apr. 🌐 The ‘Roaring Forties’—so called because the landladies and lords roar when rent is due.
1925		O.O. McIntyre ‘New York Day by Day’ 1 Oct. [synd. col.] The Roaring Forties suddenly became suspicious something was wrong.
1938		H. Asbury Sucker’s Progress 428: From about 1880 to the middle 1890’s, when they began to creep into the Roaring Forties, the most important of the first-class houses [...] were concentrated in the old Tenderloin district.