What is "meriasek"

Saint Meriasek was a 4th-century Breton saint. The legends of his life are known through Beunans Meriasek, a Cornish language play known from a single surviving manuscript copy dated 1504, and a few other sources. He is the patron saint of Camborne, and according to his legendary will his feast day is the first Friday in June (although it is celebrated in some places on June 7).