intrados

noun

in·​tra·​dos ˈin-trə-ˌdäs 

-ˌdō;

in-ˈtrā-ˌdäs

plural intrados

ˈin-trə-ˌdōz,

-ˌdäs  or intradoses ˈin-trə-ˌdä-səz 

: the interior curve of an arch see arch illustration

Word History

Etymology

French, from Latin intra within + French dos back — more at dossier

First Known Use

1772, in the meaning defined above