1. Any structure rising above the roof of a building and having apertures in its sides by which the interior of the building is ventilated or illuminated, e.g. the octagonal lantern at Ely Cathedral (1322–c.1344).
2. Any such structure whether lighting an interior or not, such as the upper part of cathedral- or church-towers, especially those treated in a light, almost transparent way, usually octagonal uppermost stages (e.g. St Botolph, Boston, Lincs. (c. 1510–20), St Mary and All Saints, Fotheringhay, Northants. (late C15), All Saints, York (late C15), and the crossing-tower of St-Ouen, Rouen, France (C15)).
3. By extension, the upper structure on top of a cupola (e.g. Florence Cathedral (C15), San Pietro, Rome (C16), and St Paul's Cathedral, London (C17)).
lan·tern / ˈlantərn/ • n. 1. a lamp with a transparent case protecting the flame or electric bulb, and typically having a handle by which it can be carried or hung: a paper lantern. ∎ the light chamber at the top of a lighthouse.2. a square, curved, or polygonal structure on the top of a dome or a room, with the sides glazed or open, so as to admit light.