Soffit

Soffit (from Fr. soffite, Ital. soffitta, a ceiling, formed as if from suffictus for suffixus, Lat. suffigere, to fix underneath), a term in architecture given to the underside of any constructional feature; as for instance that of an arch or an architrave whether supported by piers or columns; also to the underside of a flight of stairs, and in the classic entablature to the underside of the projecting cornice.