Green’s Dictionary of Slang

dealer n.

[a specific use of an 11C SE word meaning trafficker, in whatever he or she happened to deal]

1. a brothel-keeper, a bawd.

[UK]Memoirs of [...] Jane D****s 74: Alkl the gentlemen that frequent our house, allow me to be the fairest dealer in Covent-garden.

2. (US Und.) a wholesaler of counterfeit money.

[Ire]Tom And Jerry; Musical Extravaganza 53: Dealers in queer, passers of bad bills.
[US]G.P. Burnham Memoirs of the US Secret Service 92: He soon made up his mind that the dealer in the ‘queer’ rather than the ‘shover’ was the party who piled his gains with the greatest ease.
[US]G. Henderson Keys to Crookdom 402: Dealer. Wholesaler of bogus currency.

3. (drugs, also deal, John Deal) a drug seller, one with a wholesale role, as opposed to the less important pusher n. (3c)

[US]Phila. Eve. Bulletin 5 Oct. 40/4: Here are a few more terms and definitions from the ‘Racket’ vocabulary: [...] ‘pusher,’ a ‘small-time guy’ who sells for a large dealer.
[US]D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 1 in AS XI:2 120/2: dealer. A peddler. Often restricted to a druggist who is amenable to persuasion.
[US]Monteleone Criminal Sl. (rev. edn).
[UK]A. Salkey Quality of Violence (1978) 160: She knew nothing about [...] the business transactions between himself and the ganja dealers.
[UK]T. Taylor Baron’s Court All Change (2011) 31: He’s a dealer [...] He sells it’ [i.e. cannabis].
[US]H.E. Roberts Third Ear n.p.: deal n. [...] 2. one who sells drugs (John Deal).
[US]C. White Life and Times of Little Richard 149: All the hookers, hustlers, and dealers hung around there.
[UK]G. Burn Happy Like Murderers 241: The runaways and misfits coming round and the dealers, and with the dealers the busts and the Bill.
[UK]Indep. 10 Jan. 6: The drugs would come to us [...] you just had to give a local dealer a call and he’d drop it off.
[UK]K. Richards Life 203: To be a dealer you’ve got to be way in front, otherwise you slip up.