Green’s Dictionary of Slang

‘a pack of cards contrived for cheating, by cutting all the cards from the two to the seven concave, and all from the eight to the king convex. Then by cutting the pack breadthwise a convex card is cut, and by cutting it lengthwise a concave is secured’ (Hotten, 1864).

1825		C.M. Westmacott Eng. Spy I 271: The mark for every Leg and Greek, / Who play the concave suit [note] Cards cut in a peculiar manner, to enable the Leg to fleece his Pigeon securely.
1828		‘A Flat Enlightened’ Life in the West I 144: ‘I have obtained a new pack of “concave and convex” cards [...] See, the low cards are convex at the sides, and concave at the top and bottom, the high cards concave at the sides, and convex at the top and bottom . When you want to cut the packs low [...] you take the cards across for low, and lengthways for high.
1864, 1867, 1870		Hotten Sl. Dict.