Definition of passe-partout in US English:

passe-partout

noun

  • 1A picture or photograph simply mounted between a piece of glass and a sheet of cardboard (or two pieces of glass) stuck together at the edges with adhesive tape.

    • ‘You find here vendors of Cardboard for passepartouts from Germany and Russia.’
    • ‘At Halbe you have a choice of five colours and a variety of thicknesses. You can choose between 1.5 and 3 mm thick passepartouts’
    1. 1.1 Adhesive tape or paper used in making passe-partout frames.
      ‘a looking glass of passe-partout and blackened mercury’
  • 2archaic A master key.

Origin

Late 17th century: from French, literally ‘passes everywhere’.

Pronunciation

passe-partout

/ˌpaspərˈto͞o/