Beneïz
The name given to the magical drinking horn which revealed a woman’s chastity, or lack thereof, in the First Continuation of Chrétien’s Perceval.
Banded with gold and embellished with jewels, the horn spilled its wine all over a cuckold, but allowed a man with a faithful wife to drink freely. Arthur’s entire court attempted to drink from the horn, but only one, including Arthur, succeeded: Caradoc Briefbas, whose wife was called Guignier.
The same episode appears in Biket’s Lai du Cor and in numerous subsequent tales, but the horn itself is not named. Beneoiz is probably a form of the French ‘blessed‘ (benoit) and may have a connection with the blessed horn of King Bran.
See also
Chastity Test | The Legend of King Arthur
Thirteen Treasures of Britain | The Legend of King Arthur
Source
First Continuation of Chrétien’s Perceval | Attributed to Wauchier of Denain, c. 1200