E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Sixteen-string Jack.
John Rann, a highwayman, noted for his foppery. He wore sixteen tags, eight at each knee. (Hanged in 1774.)
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Dr. Johnson said that Grays poetry towered above the ordinary run of verse as Sixteen-string Jack above the ordinary foot-pad.Boswell: Life of Johnson.