Green’s Dictionary of Slang

job n.1

also jobey
[? 15C SE job, a small compact portion of some substance; a piece, lump (cf. thick ’un n.)]

a guinea, a pound.

[UK] ‘Of the Budge’ Head Canting Academy (1674) 12: And when that we have filed him / Perhaps of half a Job.
[UK]B.E. Dict. Canting Crew n.p.: Job, a Guinea, Twenty Shillings, or a Piece.
[UK]J. Hall Memoirs (1714) 12: Job a Pound.
[UK]New Canting Dict. [as cit. c.1698].
[UK]Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
[UK]Canting Academy, or the Pedlar’s-French Dict. 112: Twenty Shillings A Job.
[UK]Scoundrel’s Dict. 14: A Guiny or Job – Huskin-lour.
[UK]Grose Classical Dict. of the Vulgar Tongue.
[UK]H.T. Potter New Dict. Cant (1795).
[UK]G. Andrewes Dict. Sl. and Cant.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[UK]G. Kent Modern Flash Dict.
[UK]Flash Dict. in Sinks of London Laid Open.
[UK]Duncombe New and Improved Flash Dict. n.p.: Job or Jobey a guinea.

In phrases