FOOTMAN's Mawn'd,
an artificial Sore made with unslak'd Lime, Soap, an the Rust of old Iron, on the Back of a Beggar's Hand, as if hurt by the Bite or Kick of a Horse.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Footman’s Mawnd in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).