spandrel.
1. Quasi-triangular plane, the hanse or haunch, framed by the extrados of an arch, a horizontal line projected from the crown, and a vertical line rising from the springing, often decorated.

2. Similar plane between two arches in an arcade.

3. Web of a vault between two ribs.

4. Triangle formed between the string of a stair and the floor.

5. In a framed structure the panel between the cill of a window and the top of the window below.

6. Approximately triangular space between the curve of a brace and a post and beam in a medieval timber truss.

span·drel / ˈspandrəl/ • n. Archit. the almost triangular space between one side of the outer curve of an arch, a wall, and the ceiling or framework. ∎  the space between the shoulders of adjoining arches and the ceiling or molding above.

spandrel (archit.) space between either shoulder of an arch and the surrounding rectangular framework. XV. perh. f. AN. spaund(e)re, poss. f. espaundre EXPAND; see -EL2
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