Final answer:
A spiral ornament on a Corinthian capital is referred to as a volute, which is a distinctive scroll-shaped feature.
Step-by-step explanation:
The spiral ornament mentioned in the question is known as a volute. These are ornaments shaped like scrolls or cinnamon rolls and are a notable feature of Corinthian capitals. The Corinthian order is recognized for its ornate capitals, featuring stylized acanthus leaves that are intricately carved. In comparison to the simpler Doric and Ionic orders, the Corinthian order is the most elaborate and is characterized by its slender, vegetal elements. These voluminous and scroll-like forms are not only decorative but also serve to support the abacus of the capital, contributing to the distinct aesthetic of Corinthian architecture seen in Roman monuments like the Pantheon.