E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Oyster-shelling, blackballing, or expelling. Clisthens gave the people of Attica the power of removing from the state, without making a definite charge, any leader of the people likely to subvert the government. Each citizen wrote his vote on an earthenware table (ostracon), whence the term.