Coventry

Concise Oxford English Dictionary © 2008 Oxford University Press:
Coventry/ˈkʌvəntri/

▶noun (in phr. send someone to Coventry) chiefly Brit. refuse to associate with or speak to someone.

word history: The origins of the phrase send someone to Coventry, recorded since the 18th century, are uncertain. It is sometimes said to derive from the treatment suffered in the past by soldiers stationed in the west Midlands city of Coventry, who were unpopular with the townspeople. Alternatively, it may have arisen because Royalist prisoners were sent there during the English Civil War (1642–9): the city was held by Parliamentary forces and was thus unlikely to give the prisoners a warm welcome.