Spandrel /(?)/

Span·drel

Spandrel

n.
  1. The irregular triangular space between the curve of an arch and the inclosing right angle; or the space between the outer moldings of two contiguous arches and a horizontal line above them, or another arch above and inclosing them. (Arch.)
  2. A narrow mat or passe partout for a picture. [Cant]