Crossword clue: an approximately triangular surface area between two adjacent arches and the horizontal plane above them

The most common answer is spandrel (8 letters).

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

Possible answers

spandrel 8 letters wn-def

an approximately triangular surface area between two adjacent arches and the horizontal plane above them

spandril 8 letters wn-def

an approximately triangular surface area between two adjacent arches and the horizontal plane above them