passe-partout

Noun

passe-partout (plural passe-partouts)

1. That by which one can pass anywhere; a safe-conduct.

   Synonyms:

   safe-conduct

2. A master key.
   • The traditional (or modern) way of confronting complexity was to find a secure point of reference that could serve as foundation, a passe-partout, a master key from which everything else could be derived.1998, Paul Cilliers, Complexity and Postmodernism: Understanding Complex Systems, Psychology Press, →ISBN, page 112

   Synonyms:

   passkey

3. A light picture frame or mat of cardboard, wood, etc., usually put between the picture and the glass, and sometimes serving for several pictures.
   • A new introduction for use in conjunction with passe-partout framing is a series of corner pieces which are readily folded round the corners of the finished passe-partout, giving it a certain added effect and slight embellishment.1933, William Crookes, T. A. Malone, George Shadbolt, J. Traill Taylor, William Blanchard Bolton, Thomas Bedding, The British Journal of Photography

   Synonyms:

   mat, matting