The Slipped Waistcoat
Two options seem to be canvassed for the origin and purpose of slips, one being that they are a vestige of the under-waistcoat popular during the Regency period in Britain, when I understand it was fashionable to wear a number of waistcoats one over the other, with each just showing. Another explanation is that the slips were designed to guard against non-fast dyes from black waistcoats bleeding onto the shirt front. They seem to have died out more or less by the Second World War, except amongst the diehards.  They can still be seen worn with morning dress on rare occasions, sported by such persons as the Lord Lieutenant of Durham and, most recently, HRH Prince Charles.
Close-up of waistcoat shewing slip
The slip itself
A slipped waistcoat with braided edges
Slipped waistcoat open, shewing details of slip
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