E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To send one to Coventry. To take no notice of him; to let him live and move and have his being with you, but pay no more heed to him than to the idle winds which you regard not. According to Messrs. Chambers (Cyclopdia), the citizens of Coventry had at one time so great a dislike to soldiers that a woman seen speaking to one was instantly tabooed. No intercourse was ever allowed between the garrison and the town; hence, when a soldier was sent to Coventry, he was cut off from all social intercourse.
Hutton, in his History of Birmingham, gives a different version. He says that Coventry was a stronghold of the parliamentary party in the civil wars, and that all troublesome and refractory royalists were sent there for safe custody
The former explanation meets the general scope of the phrase the better. (See BOYCOTT.)