soffit
Concise Oxford English Dictionary © 2008 Oxford University Press:
soffit /ˈsɒfɪt/
▶noun the underside of an architectural structure such as an arch or balcony.
– origin C17: from Fr. soffite or Ital. soffitto, based on L. suffixus ‘fastened below’.
'soffit' also found in these Oxford entries:

