CARRIERS,
a Set or Rogues, who are employ'd to look out, and whatch upon the Roads, at Inns, &c. in order to carry Information to their respective Gangs, of a Booty in Prospect.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
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Carriers in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).