What is "ternan"

Saint Ternan (fifth century?) is venerated as the "Bishop of the Picts." Not much is known of his life. He may have been consecrated by St. Palladius. Some scholars believe that he may have been a monk at Culross, which had been founded by St. Serf, and that he was a contemporary of Serf. Others state that he was a follower of St. Ninian.