What do film cameos and cameo brooches have in common?

Why are film cameos called cameos? In which sense do they resemble cameo brooches? In both meanings of the word we have a human figure. Are they similar in their brevity of appearance? In their ornamental function? In their silence and hieratic attitude? Or are they comparable in their value (jewels are valuable, famous people are important)?

I have already checked several etymological sources. They differ. I’m looking for your opinion. In what do you think film cameos and cameo brooches are similar? What do you feel is the key element in common?

To try to further clear my question: I’m debating in another (Spanish-language) forum the anglicism “cameo”, which Spaniards use but ignore is related to cameo jewels (“camafeos” in Spanish). To most Spaniards cameo means nothing except cameo films. I’m trying to find out the connotations anglophones bring to their mind when they use the word in the cinematographic sense, connotations that Spaniards are unaware of, to show how in this specific case (not in most others) the adoption of this anglicism is not enriching Spanish language.

But maybe this is not a good question anyway.

Solution 1:

You're on the right track; this is a very good website to check such matters:

cameo (n.) early 15c., kaadmaheu, camew, chamehieux and many other spellings (from early 13c. in Anglo-Latin), "carved precious stone with two layers of colors," from Old French camaieu and directly from Medieval Latin cammaeus, of unknown origin, perhaps ultimately from Arabic qamaa'il "flower buds," or Persian chumahan "agate." Transferred sense of "small character or part that stands out from other minor parts" in a play, etc., is from 1928, from earlier meaning "short literary sketch or portrait" (1851), a transferred sense from cameo silhouettes.