Definition: Arillary refers to a type of architectural element used in stucco, which has been shaped with rounded corners or arched sides to create visual interest and enhance structural integrity. It's often seen on buildings like domes and arches, serving as a decorative feature. Definition: The term "arillary" comes from the Latin word "arilla," meaning a rounded edge in a geometric shape, and it refers to an architectural element used in stucco to create visual interest and enhance structural integrity.