ingler, n. — Green’s Dictionary of Slang

ingler n.

[? dial. ingle, to fondle; thus he ‘fondles’ the horse to persuade it to go with him. Note SE ingle, a catamite]

a horse thief who toured country fairs looking for victims.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: ingler horse-dealers of suspicious character.
1809		G. Andrewes Dict. Sl. and Cant.
1821		Flash Dict.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
c.1850		Duncombe New and Improved Flash Dict.
1859		Matsell Vocabulum.