Green’s Dictionary of Slang

1. (UK Und.) a successful highwayman [SE snaffle, a light bridle + snaffle v. (2)].

1608		Dekker Lanthorne and Candle-Light Ch. 7: He that never alights off a rich Farmer or countrie Gentleman, till he haue drawne money from him, is calld The Snaffle.
c.1698		B.E. Dict. Canting Crew n.p.: Snaffle, a Highwayman that has got Booty.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant n.p.: Snaffle highwayman.
1811		Lex. Balatronicum.
1821		Flash Dict. [as cit. 1809].
1835		G. Kent Modern Flash Dict. [as cit. 1809].
1848		Flash Dict. in Sinks of London Laid Open 125/1: Shaffle [sic], highwayman.
c.1850		Duncombe New and Improved Flash Dict.
1859		Matsell Vocabulum 82: snafflers Highwaymen.

2. in senses of incomprehensible or constrained speech, as if subject to a snaffle.