word of the week: COFFER
COFFER: one of a number of sunken panels (usually in the shape of a square, rectangle, or octagon) in a ceiling, soffit or vault. A coffered ceiling usually has a purely decorative purpose, but can also have a more practical purpose in lightening the load of a ceiling or dome as seen below at the Pantheon in Rome.
To the right is one of many coffered ceilings at the Chicago Cultural Center. A coffered ceiling can also be called a lacunar ceiling.