Green’s Dictionary of Slang

a cow-stealer.

1663		Wandring whores complaint n.p.: The ninteenth [sic] a Donnaker that will make vows / To go in the Country and steal all the Cows.
1669		Nicker Nicked in Harleian Misc. II (1809) 108: There come in shoals of hectors, trepanners, [...] bulkers, droppers, gamblers, donnakers, cross-biters.
1671		‘L.B.’ New Academy of Complements 205: The seventeenth a Dun-aker, that will make vows, / To go to the Countrey and steal all the Cows.
1693		Poor Robin [as cit 1669].
c.1698		B.E. Dict. Canting Crew.
1712		‘Black Procession’ in Farmer Musa Pedestris (1896) 39: The seventeenth a dunaker, that stoutly makes vows, / To go in the country and steal all the cows.
1725		New Canting Dict. n.p.: dunaker a Stealer of Cows, or Calves, &c. The Forty-third Order of Villains.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1859		Matsell Vocabulum.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1895		Crowe Aus. Sl. Dict. 26: Dunneker, a cattle-thief.