to exclude someone from a group or society, usually by common consent of the group's members;
e.g. They were looking for a new reason to ostracize her, and the incident offered them one.
(verb)
in ancient Greece, to temporarily exile or banish someone from the city by popular vote, without special accusation or trial, i.e. to subject someone to the process of ostracism;
e.g. The people voted to ostracize him when he became overly powerful.