noun, plural ex·tra·dos [ek-struh-dohz, ek-strey-dohz] /ˈɛk strəˌdoʊz, ɛkˈstreɪ doʊz/, ex·tra·dos·es. Architecture.
Examples from the Web for extrados
The lower surface or soffit of the arch is the intrados, E, and the upper surface the extrados, F.
The Tuscan arch, where the extrados takes the form of a pointed arch.
The form of the mound may be described as reproducing the extrados of a depressed arch.A History of Art in Chalda & Assyria, v. 1|Georges Perrot
The under or concave side of the voussoirs is called the intrados, and the upper or convex side the extrados of the arch.
This arch was roughhewn on the flat surfaces and on about half of the outer curved surface, or extrados.The Cultural History of Marlborough, Virginia|C. Malcolm Watkins