Final answer:
A pilaster is a distinct, slender, vertical masonry feature engaged in a wall or pier that supports or feigns to support an arch or ribbed vault.
Step-by-step explanation:
The distinct, slender, vertical masonry feature engaged in a wall or pier, supporting or feigning to support an arch or a ribbed vault is called a pilaster. Pilasters are shallow, flattened out columns attached to a wall, typically used for decorative purposes rather than providing structural support.