Definition of extrados in US English:

extrados

noun

Architecture
  • The upper or outer curve of an arch.

    Often contrasted with intrados
    • ‘It is quite natural to obtain greater values at the intrados and smaller ones at the extrados since the inside fiber of the pipe is under compression while at the same time the outside fiber is under tension, during bending.’
    • ‘The outer boundaries of a voussoir are the extrados.’

Origin

Late 18th century: from French, from Latin extra ‘outside’ + French dos ‘back’ (from Latin dorsum).

Pronunciation

extrados

/ˈekstrəˌdäs//ˈɛkstrəˌdɑs/