Meaning A girl's name of Latin origin, it means "Only child; also can be a variant of Una: One." Origin of Oonagh Latin , Celtic Popular Middle Names Pronunciation 🔊 Listen Oonagh oon-agh Similar Names Aurene Septima Sheelagh Annabell Orial Oribel Oribella Okelani Mari Tiffanie Year by Year Popularity of Oonagh