Sentence:  A <WSD>soffit</WSD> is the underside of any part of a building's structure. Most people know about the <WSD>soffit</WSD> boards below their fascia boards (which cap off the ends of a roof's rafters). But if you walk through a brick-built tunnel and glance upwards, for example, you will be looking at the <WSD>soffit</WSD> of the arch. 
Meaning of the word marked with <WSD> tags:  The visible underside of an arch, balcony, beam, cornice, staircase, vault or any other architectural element.