Green’s Dictionary of Slang

1. a sucking pig [euph.].

1621		Jonson Gypsies Metamorphosed 516: From an oyster and fryd fishe A sowes babie in a dishe.
c.1698		B.E. Dict. Canting Crew n.p.: Sow’s baby a Pig.
1725		New Canting Dict. [as cit. c.1698].
c.1750–1882		B.M. Carew Life and Adventures.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1819		‘One of the Fancy’ Tom Crib’s Memorial to Congress xxviii: A sow’s baby, a pig.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.

2. sixpence (2½p), occas. a shilling (5p) [sixpence is smaller than a hog n. (1a), i.e. a shilling].

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue .
1811		Lex. Balatronicum.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict. 200: PIG or sow’s baby, a sixpence.
1873		Sl. Dict.
1881		Morn. Bulletin (Rockhampton, Qld) 18 July 2/6: For our next coin in value [i.e. sixpence] twenty names are found [...] ‘Fyebuck,’ ‘half-hog,’ ‘kick,’ ‘lord of the manor,’ ‘pig,’ ‘pot,’ ‘say saltee,' ’sprat,’ ‘snid,’ ‘simon,’ ‘sow's baby,’ ’tanner,’ tester,’ and ‘tizzy’.
1885		Household Words 20 June 155: The sixpence... is variously known as a ‘pig,’ a ‘sow’s baby,’ a grunter, and ‘half a hog’ [F&H].
1922		Dundee Eve. Teleg. 19 July 2/4: Sixpence is a popular coin in slangdom [...] ‘half-a-hog,’ ‘kick,’ (thus two and a ‘kick’ 2s 6d)‘lord of the manor,’ ‘pig,’ ‘pot,’ ‘snid,’ ‘sow’s baby’.