What is "cynfarwy"

Cynfarwy was a Christian in the 7th century about whom little is known. He was venerated by the early church in Wales as a saint, although he was never formally canonised. St Cynfarwy's Church in Anglesey is dedicated to him, and his name is also preserved in the name of the settlement around the church, Llechgynfarwy (or sometimes "Llechcynfarwy"). His feast day is in November, although the date varies between sources.