Green’s Dictionary of Slang

a prostitute.

a.1680		Royoter’s Ruine [broadside ballad] I’ll make a clear end and spend that on a Whore. / And as along in the streets he was walking / He chanced with one of his Mobs to meet.
1725		New Canting Dict. n.p.: mob or mab a Wench or Harlot.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. n.p.: [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue [as cit. 1725].
1811		Lex. Balatronicum [as cit. 1725].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1725].
1859		Matsell Vocabulum 53: mab A harlot.