Green’s Dictionary of Slang

1. (UK Und.) the backside.

1674		Head Canting Academy (2nd edn).
c.1698		B.E. Dict. Canting Crew n.p.: Cracker, c. an Arse.
1725		New Canting Dict.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.

2. (S.Afr.) in pl., sheep-skin trousers.

1833		C.G.H. Literary Gazetter 2 Sept. 238: Old Crackers alias leather breeches.
1845		Autobiog. of Sir Harry Smith II 348: You [...] would laugh to see our motley group, with every costume of a mean kind [...] the 72nd’s men with crackers.
1889		H.A. Bryden Kloof and Karroo 199: Klaus looked pretty well ‘baked’ even in his old leather ‘crackers’.
1913		C. Pettman Africanderisms 131: Crackers Trousers of prepared sheep-skin, largely used in the early days by the settlers, and so named because of the cracking noise which they made at every move of the wearer.