Ostracism : Refers to the procedure of expelling a citizen from the city/estate for reasons like political rivalry. Ostracism doesn’t have a relation to the process of justice.
Origination : from ancient Greek word, ὀστρακισμός, ostrakismos. Which explained the procedure of expelling a citizen for ten years for reasons like expressing political anger at a victim.
Reference : http://en.wikipedia.org/wiki/Ostracism