passe-partout

UK: English: /ˌpæspɑːˈtuː/, French: /pɑspartu/

US: (pas′pär to̅o̅′; Fr. päs par to̅o̅′)

Inflections of 'passe-partout' (n): npl: passe-partouts

WordReference Random House Unabridged Dictionary of American English © 2025

passe-par•tout  (pas′pär to̅o̅′; Fr. päs par to̅o̅′), n., pl. -touts 

(-to̅o̅z′; Fr. -to̅o̅′). 
1. something that passes everywhere or provides a universal means of passage.
2. a master key;
   skeleton key.
3. an ornamental mat for a picture.
4. a method of framing in which a piece of glass is placed over a picture and is affixed to a backing by means of adhesive strips of paper or other material pasted over the edges.
5. paper prepared for this purpose.

• French: literally, (it) passes everywhere
• 1635–45

Collins Concise English Dictionary © HarperCollins Publishers::

passe-partout / ˌpæspɑːˈtuː pɑspartu/ noun

1. a mounting for a picture in which strips of strong gummed paper are used to bind together the glass, picture, and backing
2. the gummed paper used for this
3. a mat, often decorated, on which a picture is mounted
4. something that secures entry everywhere, esp a master key

Etymology: 17th Century: from French, literally: pass everywhere