We need an architecture historian here...

You rang, my dear? The problem with architectural words is that it is often so hard to decide exactly what a particular building feature should be called because different authorities use different rules. Cupola/lantern is one such tricky divide: a lantern is usually considered a cupola with windows and no floor, so it can light the interior of the building, but some call any cupola with windows a lantern, and others don't call anything a lantern and stick with cupola. The exact dividing line between a bay window and an oriel is equally tricky to spot.