ˈekstrəˌdäs, -ˌdōs, -ˌdō; ekˈstrā]ˌdäs, -rä], ]_dəs noun
( plural extrados -ˌdōz ; or extradoses -äsə̇z, -ōsə̇z, -əsə̇z\)
Etymology: French, from Latin extra outside + French dos back — more at extra- , dossier
1. : the exterior curve of an arch ; specifically : the upper curved face of the body of voussoirs which forms the arch
2. : the outer surface of a vault — compare intrados