Green’s Dictionary of Slang

1. (US) extreme, utter, complete.

1867		G.W. Harris ‘Sicily Burn’s Wedding’ Sut Lovingood’s Yarns 87: Ole Bullen’s pint is a durn’ed fust rate, three bladed, dubbil barril’d, warter-proof, hypockracy, an’ a never-tirein appertite fur bal’-face.
1872		‘Mark Twain’ Innocents at Home 357: There’ll be a double-barreled inquest here when this trial’s off.
1885		Bulletin (Sydney) 17 Jan. 6/4: Prince Albert, who was of inferior rank, and who [...] was a double-barrelled pauper by the side of His Grace the Dook of Brunswick.
1896		Farmer Vocabula Amatoria (1966) 87: Être cul par dessus tête [...] said of a woman whose tail is oftener in the air than her head; and, specifically, of a double-barrelled harlot.
1908		E.S. Sorenson Quinton’s Rouseabout and other Stories 214: Bluff you – you double-barrelled idiot, come in an’ see!
1948		G.H. Bean Yankee Auctioneer 26: On one occasion the stunt was double-barreled.
1958		E. Gilbert Vice Trap 15: I took a good one [...] I sat back, feeling pretty double-barrelled.
1966		H.S. Thompson Hell’s Angels (1967) 44: One week later came the Time-Newsweek double-barrelled blast that really put the Angels over the top.

2. used of a woman, enjoying simultaneous vaginal and anal intercourse.

1890–1904		Farmer & Henley Sl. and Its Analogues.
1950		Goldin et al. DAUL 61/1: Double-barreled. Skilled in degeneracy, especially applied to loose women.

3. used of a lesbian, e.g. double-barrelled broad.

1939		H. Miller Tropic of Capricorn (1964) 96: She has the loose, jaunty swing and perch of the double-barrelled sex.
1968		J. Colebrook Cross of Lassitude 155: Beppo is a ‘bull-dagger,’ a ‘low dyke,’ a ‘lady-lover,’ a ‘Les-wolf,’ and a ‘double-barreled broad’.