"keen as a cameo"
A shell cameo
Creative Commons Attribution Share AlikeA shell cameo - Credit: Matteo Pedani

Cameo is a style of carving that produces a raised image, often a different colour to its background.

Cameos in Victorian times were little portraits of the profiles of men and women presented in oval frames. They were sometimes worn as pendants or brooches.

The modern use of the word, to mean a brief appearance by a recognized individual on screen or stage, derives from the cameo brooch.