a charter of liberty and political rights obtained from King John of England by his rebellious barons at Runnymede in 1215, which came to be seen as the seminal document of English constitutional practice.
(as noun a Magna Carta) a document establishing important rights or principles in a specified area:a Magna Carta for environmental protection
from medieval Latin, 'great charter'
Magna Carta in other Oxford dictionaries
Definition of Magna Carta in the US English dictionary