prettygoodword | spandrel

spandrel or spandril (SPAN-druhl) - n., the approximately triangular surface bounded by the outer curve of an arch and an adjacent straight-side figure bounding it; the surface between two adjacent arches and the horizontal cornice above them; a triangular space under a stair, or the material that fills the space; a horizontal, usually decorated member between the windows of each story of a tall building; the space, or the decoration within it, on a stamp between an oval figure and the corner.

Two spandrels marked S (thanks, Merriam-Webster). Lots of space-filling uses between a curve and a bounding rectangle. Used since the 15th century as spandrell, from Anglo-French spaunder, probably from espandre, to spread out, from Latin expandere, to expand.

---L.