Green’s Dictionary of Slang

(US Und.) a gambling house or room where all games are invariably corrupt.

1870		Eve. Teleg. (Phila., PA) 1 Feb. 5/1-2: The Brace or Skin Faro Banks. [...] The term brace or skin is applied to houses where the robbing game only is used, where it impossible to win, and where the dealer can take your money if he chooses [...] There are in this city at present only two houses conducted as brace houses, although there is no house that that will not and does not at certain times and under certain circumstances take advantage of players, especially if they are uninformed and ignorant .
1873		J. O’Connor Wanderings of a Vagabond 183: Let us now take a peep into the brace room, while the steerer and his victim are on their way to it. [Ibid.] 207: If some of these sharpers fit up and furnish their ‘brace’ rooms on a grander scale than others, it is only to give to them a more respectable appearance. [Ibid.] 212: Pittsburgh, Toledo, Columbus [...] Providence, and other cities of the same size, have at least one ‘brace-house’ each.
1881		St Louis Post-Dispatch (MO) 3 Jan. 2/4: There are many brace faro games in St Louis, but none is probably better known to the police and sporting men generally than Hank Wider’s [...] brace house at No. 9 S. Fifth street.
1899		(ref. to 1866-68) Inter Ocean (Chicago) 3 Sept. 17/7: Gambling in the old Days [...] It was one of two brace houses and the fellers that worked there was so crooked that the slept in beds made in the shape of the letter S.