Green’s Dictionary of Slang

1. that member of a criminal gang who either carries information between gang members or carries away the proceeds of a robbery, of pickpocketing etc.

1725		New Canting Dict. n.p.: carriers, a Sett of Rogues, who are employ’d to look out, and watch upon the Roads, at Inns, &c. in order to carry Information to their respective Gangs, of a Booty in Prospect.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1938		(ref. to 1910s) F.D. Sharpe Sharpe of the Flying Squad 171: Another member of the gang is known as the ‘Carrier.’ His job is to get away with the wallet which is handed to him by the ‘tool’ the moment it is stolen.
1950		P. Hoskins No Hiding Place! 190/1: Carrier. Man who actually secretes a wallet after it has been stolen by the pickpocket.

2. a thigh.

1753		J. Poulter Discoveries (1774) 29: They will open a Piece of Stuff and hold it up between the Owner and their Partner that sits down with her Petticoats half up ready for the Word nap it; then she puts it between her Carriers (that is, a Cant Word for Thighs) and then gets up and lets her Clothes drop [...] and so walks off.
1786		Whole Art of Thieving .

3. (UK und.) a middleman for a team of counterfeiters.

1935

Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 2: Carrier: Person who carries base coin and keeps utterer supplied.

4. (US drugs) a distributor of drugs.

1953

Anslinger & Tompkins Traffic In Narcotics 306: carrier. A distributor of drugs to addicts.