A blockhead, or stupid fellow. We three loggerheads be: a sentence frequently written under two heads, and the reader by repeating it makes himself the third. A loggerhead is also a double-headed, or bar shot of iron. To go to loggerheads; to fall to fighting.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Locksmith’s Daughter * LollNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes