COLT,
an Inn-keeper that lends a Horse to a Highway-man, or to Gentleman Beggars; also a Lad newly initiated into Roguery.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Colt in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).