<p><strong>Noun</strong></p><ul><li>any of various objects or spaces of crescentlike or semicircular outline or section</li><li>Architecture: (in the plane of a wall) an area enframed by an arch or vault</li><li>a painting, sculpture, or window filling such an area</li><li>Fortification: a work consisting of a salient angle with two flanks and an open gorge</li><li>Ordnance: a towing ring in the trail plate of a towed vehicle, as a gun carriage</li><li>Ecclesiastical: Luna (def 3)</li></ul>