extrados
Pronunciation: /ˈekstrəˌdäs
noun (plural same or extradoses)
Architecture
The upper or outer curve of an arch. Often contrasted with intrados.
Origin
late 18th century: from French, from Latin extra 'outside' + French dos 'back' (from Latin dorsum).
Archie gazed lovingly at the doorway. No simple lintel squared across the top. Instead, there was the sturdy curve of voussoirs, the wedged stones which made the arch over the entrance. Archie especially liked it when the "extrados", the upper surfaces of each stone, were extended from the building's face with decorative carvings in the stone.
[The wings of an airplane have the term extrados applied to the upper, curved surface, too.]
See a good illustration by photographer Dauvit Alexander
