Said originally to mean one whose skin or hair had fallen off from some disease, chiefly the venereal one; but now commonly used by persons speaking of themselves: as, there stood poor pill garlick: i.e. there stood I.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Pilgrim’s Salve * PillalooNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes