Green’s Dictionary of Slang

cool n.1

[ety. unknown; ? his ‘coolness’ when thieving; or Fr. cul, the buttocks, near which the purse hung]

(UK Und.) a cut-purse.

[UK]Greene Second Part of Conny-Catching in Grosart (1881–3) X 110: It fortuned that a Nip and his staul drinking at the three Tuns in Newgate market, sitting in one of the roomes next to the streete, they might perceiue wher a meale man stood selling of meale, and had a large bag by his side, where by coniecture there was some store of mony: the old Coole, the old cut-purse I mean, spying this, was delighted with the shew of so glorious an object.