Green’s Dictionary of Slang

1. (US) nonsense, humbug.

1864, 1867, 1870		Hotten Sl. Dict. 156: Hornswoggle nonsense, humbug. Believed to be of American origin.
1873		Sl. Dict.
1956		C. Neider Authentic Death of Hendry Jones 42: That’s hornswoggle.

2. (US) an act of surpassing or confusing; a confidence trick .

1877		Dodge City Times (KS) 1 Sept. 8/2: A social game of ball [...] which resulted in a scientific horn-swaggle of the Vances, or in other words the Vance’s scored 4 to the Blue Stockings’ 19.
1974		Akron Beacon Jrnl 11 Jan. 10/1: The Sting [...] There’s a vain, bullying Irish mobster [...] who’s just begging to be taken by any confidence men nervy enough. Well, Paul Newman and Robert Redford [...] are just the boys to handle a good hornswaggle.
1991		L.A. Times 25 Aug. mag. 11/3: Vintage Pogo-ese locutions such as ’They done perpetrated a baldfaced hornswaggle’.

3. (US) a trickster, a charlatan.

1908		Times (Munster, IN) 2 Apr. 4/2: Some of them think Taft has been horswaggled. Nix. Bill knows a hornswaggle by heart and can juggle him without a net.
1983		Boston Globe (MA) TV Week 13-19 Mar. 9/1: An old hand named Angelica is trying to break him in while a devilish Hornswaggle aims to break him down.