The most common and most likely answer to this crossword clue is the 8 letter word BANISHED
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The straight part
We know that "ostracised" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ostracised = banished.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BANISHED mean?
BANISHED verb- (heading) To send someone away and forbid that person from returning.
- To expel, especially from the mind.
- Having been subject to banishment; kicked out and forbidden from returning; forbidden and prohibited.