A family’s tribe or brotherhood; a word much used in Scotland. The head of the clan; the chief: an allusion to a story of a Scotchman, who, when a very large louse crept down his arm, put him back again, saying he was the head of the clan, and that, if injured, all the rest would resent it.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1736 dictionary of canting and thieving slang.
Clammed * ClankNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes