When I learned the word "ostracise" in the seventh grade,
the book said that "shells" were marked by voters.
And the root of the word meant "shell (of sea clams,etc.)
but when there were as many as seven thousand of these
required, it was obviously easier to substitute broken
pieces of pottery. So the word was then applied to pottery
sherds.

oyster ['ɔýstə]
noun
1 a any edible marine bivalve mollusc of the genus Ostrea, having a rough irregularly shaped shell and occurring on the sea bed, mostly in coastal waters
b (as modifier)
example: oyster farm
example: oyster knife


2 any of various similar and related molluscs, such as the pearl oyster and the saddle oyster (Anomia ephippium)

3 the oyster-shaped piece of dark meat in the hollow of the pelvic bone of a fowl

4 something from which advantage, delight, profit, etc., may be derived
example: the world is his oyster

5 (informal)
a very uncommunicative person
verb
6 [intransitive] to dredge for, gather, or raise oysters
[ETYMOLOGY: C14 oistre, from Old French uistre, from Latin ostrea, from Greek ostreon; related to Greek osteon bone, ostrakon shell]

Here's a URL I found about ostracism:
http://216.239.53.104/search?q=cache:UWx_S8f4QkcJ:www.classics.umd.edu/Latinday/Ostracism.pdf+Aristides+ostracism&hl=en&ie=UTF-8

I just told taught this word to my kids a few weeks ago while I was relating what I had learned about Themistocles from the history channel. Great story for anyone with an hour to blow.

k

In reading more about ostracism, I encountered the word
"proxeny". I haven't yet found the definition, but here's the quote:
"Theopompos in the Tenth Book of the Philippika says about Kimon: 'When five years had not yet gone by, a war having broken out with the Lacedaemonians, the People sent for Kimon, thinking that by his proxeny he would make the quickest peace. When he arrived at the City, he ended the war."
I'm guessing it means his friends among the enemy.

I found this:
"There was an institution -particularly in Greece- that introduced this private pact between strangers into the public domain: proxeny.
Proxenia was a contract between a State and the citizen of a polis. The latter, chosen among the most influential and wealthy personalities of his city, was a sort of godfather of a foreign State and its citizens. He would welcome, at his own expense, the travellers or the ambassadors who would arrive from the other country; he would sponsor them and represent them in the circumstances of religious ceremonies and commercial intercourses. In exchange, he would benefit of honours and privileges, mostly symbolical, from the nation with which he would have signed the pact.

pro, for + xenos, stranger; loosely, hospitality to those who came from a friendly city or state

Gk xenos 'stranger, guest' is from the zero-grade of the PIE root *ghos-, i.e., *ghs-we-no- (with some augmentation). Same root (*ghos-ti-) we get host (via Latin) and guest (from Germanic) from.

http://www.bartleby.com/61/roots/IE167.html