Magna Charta

British constitutional charter which limited the power of kings and was signed by King John I in 1215; constitution ensuring rights and liberties

Magna Carta (Latin for "Great Charter", literally "Great Paper"), also called Magna Carta Libertatum ("Great Charter of Freedoms"), is an English charter originally issued in 1215. Magna Carta was the most significant early influence on the extensive historical process that led to the rule of constitutional law today. Magna Carta influenced many common law and other documents, such as the United States Constitution and Bill of Rights, and is considered one of the most important legal documents in the history of democracy.
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Noun
1. the royal charter of political rights given to rebellious English barons by King John in 1215
(synonym) Magna Carta, The Great Charter
(hypernym) royal charter
(classification) United Kingdom, UK, Great Britain, GB, Britain, United Kingdom of Great Britain and Northern Ireland

Magna Charta, British constitutional charter which limited the power of kings

The great Charter, so called, obtained by the English barons from King John, A. D. 1215. This name is also given to the charter granted to the people of England in the ninth year of Henry III., and confirmed by Edward I.
  

Hence, a fundamental constitution which guaranties rights and privileges.