Final answer:
The architectural feature designed to shed rainwater on a buttress is known as weathering. Option D is correct.
Step-by-step explanation:
The architectural feature on a buttress or projecting pier designed to shed rainwater with a sloping top is known as weathering. This feature is essentially a sloping layer on top of the buttress engineered to direct water away from the structure, preventing erosion and water damage.
In the context of Gothic architecture, where buttresses, specifically flying buttresses, became an iconic element, the ability to shed water was essential. These flying buttresses transferred the heavy weight of stone roofs through their arches into the ground, which allowed for taller, thinner walls punctuated with large stained glass windows for increased illumination inside Gothic cathedrals.
Having proper weathering ensured the longevity and stability of the mighty architectural feats such as the Sainte-Chapelle in Paris, featuring soaring walls of stained glass supported by external flying buttresses adorned with pinnacles resembling a crown atop the structure.
This sloped surface assists in directing water away from the structure, which is vital in Gothic architecture where flying buttresses support the thin walls and large stained glass windows of cathedrals like Sainte-Chapelle.