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]