Green’s Dictionary of Slang

whoaball n.

a milkmaid.

c.1698		B.E. Dict. Canting Crew n.p.: Whow-ball, a Milk-maid.
1699		N. Ward London Spy XIII 308: [She] was as Angry when we spoke to her, as a Milk-Maid when you cry Wo-ball.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Whow-ball, a milkmaid, from their frequent use of the word whow, to make the cow stand still in milking. Ball is the supposed name of the cow.
1809		G. Andrewes Dict. Sl. and Cant n.p.: Wo ball a milk woman.
1811		Lex. Balatronicum [as cit. 1785].
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 194: Who-bawl — a milk-woman, calling to her cows; and, by refraction, she herself.
1835		G. Kent Modern Flash Dict. [as cit. 1809].
1848		Flash Dict. in Sinks of London Laid Open.
c.1850		Duncombe New and Improved Flash Dict.
1859		Matsell Vocabulum 96: woball A milkman [sic].
1895		Crowe Aus. Sl. Dict. 97: wobal, a milkman [sic].