intrados
Concise Oxford English Dictionary © 2008 Oxford University Press:
intrados /ɪnˈtreɪdɒs/
▶noun Architecture the lower or inner curve of an arch. Contrasted with extrados.
– origin C18: from Fr., from intra- ‘on the inside’ + dos ‘the back’ (from L. dorsum).
'intrados' also found in these Oxford entries:

