AUNT,
a Bawd, or Procuress; a Title of Eminence for the Senior Dells, who serve for Instructresses, Midwives, &c., to the Morts.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
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Aunt in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).