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 Ona Nuala Mia Mitzi Annabella Jill Auriol Sheelagh Shelagh Tiffany Year by Year Popularity of Oonagh