extrados
Concise Oxford English Dictionary © 2008 Oxford University Press:
extrados /ɪkˈstreɪdɒs, ɛk-/
▶noun Architecture the upper or outer curve of an arch. Contrasted with intrados.
– origin C18: from Fr., from L. extra ‘outside’ + Fr. dos ‘back’.
'extrados' also found in these Oxford entries:

