Green’s Dictionary of Slang

‘one whose scrotum is relaxed as to be longer than his penis’ (Grose, 1785).

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Rantallion. One whose scrotum is so relaxed as to be longer than his penis, i.e. whose shot pouch is longer that the barrel of his piece.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.