extrados

[ ek-struh-dos, -dohs, ek-strey-dos, -dohs ]

/ ˈɛk strəˌdɒs, -ˌdoʊs, ɛkˈstreɪ dɒs, -doʊs /

the exterior curve or surface of an arch or vault.

Also called back.

Compare intrados.

Origin of extrados

1765–75; < French, equivalent to extra- extra- + dos back (< Latin dorsum dorsum

The lower surface or soffit of the arch is the intrados, E, and the upper surface the extrados, F.

Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 |Various
The Tuscan arch, where the extrados takes the form of a pointed arch.

Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4 |Various
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.

The New Gresham Encyclopedia. Vol. 1 Part 2 |Various

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

extrados

/ (ɛkˈstreɪdɒs) /

architect the outer curve or surface of an arch or vault Compare intrados

C18: from French, from extra- + dos back, from Latin dorsum