extrados

noun

ex·​tra·​dos ˈek-strə-ˌdäs 

-ˌdō;

ek-ˈstrā-ˌdäs

plural extradoses ˈek-strə-ˌdä-səz  or extrados ˈek-strə-ˌdōz  -ˌdäs 

: the exterior curve of an arch see arch illustration

Word History

Etymology

French, from Latin extra + French dos back — more at dossier

First Known Use

1772, in the meaning defined above