To send someone to Coventry is an English idiom meaning to deliberately ostracise someone. Typically, this is done by not talking to them, avoiding their company, and acting as if they no longer exist. Victims are treated as though they are completely invisible and inaudible. The Coventry in the phrase is the cathedral city in the West Midlands.
The origins of this phrase are unknown, although it is quite probable that events in Coventry in the English Civil War in the 1640s play a part. One hypothesis as to its origin is based upon The History of the Rebellion and Civil Wars in England, by Edward Hyde, 1st Earl of Clarendon. In this work, Clarendon recounts how Royalist troops that were captured in Birmingham were taken as prisoners to Coventry, which was a Parliamentarian stronghold. These troops were often not received warmly by the locals.
A book entitled Lives of the Most Remarkable Criminals (1735) states that Charles II passed an act "whereby any person with malice aforethought by lying in wait unlawfully cutting out or disabling the tongue, putting out an eye, slitting the nose or cutting off the nose or lip of any subject of His Majesty......shall suffer death." This was called the Coventry Act, after Sir John Coventry MP, who had "had his nose slit to the bone" by attackers.
Some have suggested that the idiom derives from the ostracism that became a fate of legendary Coventry's "Peeping Tom". However it is surprising that there is no recorded use between the 1050s (the origin of the tale) and the first possible example suggested by the Oxford English Dictionary, dated 1647. Furthermore, there is no support for this derivation in Brewer's Dictionary of Phrase and Fable (1981), the Oxford English Dictionary (1986), or Partridge's Dictionary of Slang and Unconventional English (1961).
An early example of the idiom is from the Club book of the Tarporley Hunt (1765):