Meaning A boy's name of Celtic origin, it means "Mythical son of Euroswydd." Origin of Efnisien Celtic , Irish +-100%Zoom level changed to 1 Popular Middle Names Pronunciation 🔊 Listen Efnisien Similar Names Nisien Powell Connla Aod Cradawg Ferehar Glifieu Gruddieu Medredydd Sugn Year by Year Popularity of Efnisien