Persons who contract to unload ships; also thieves who lurk about wharfs to pilfer goods from ships, lighters, &c.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
To Lump the Lighter * LumpingNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes