early 15c., kaadmaheu, camew, chamehieux and many other spellings (from early 13c. in Anglo-Latin), "engraving in relief upon a precious stone with two layers of colors" (such as onyx, agate, or shell) and done so as to utilize the effect of the colors, from Old French camaieu and directly from Medieval Latin cammaeus, which is of unknown origin, perhaps ultimately from Arabic qamaa'il "flower buds," or Persian chumahan "agate."
In 19c. it also was used of other raised, carved work on a miniature scale. The transferred sense of "small character or part that stands out from other minor parts" in a play, etc., is from 1928, from an earlier meaning "short literary sketch or portrait" (1851), a transferred sense from cameo silhouettes. A cameotype (1864) was a small, vignette daguerreotype mounted in a jeweled setting.