Spān'drel, n.

noun

n. [Eng. span, O. Eng. spande.] (Arch.) 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 an horizontal line above them, and inclosing them.

An architectural diagram showing a pointed arch with spandrels shaded at its upper corners.
s s, Spandrels.