Siobhan is the Irish form of Joan — from the Hebrew Yochanan, meaning "God's grace." Joan and John share the same Hebrew root. The Irish spelling Siobhán (with the accent) reflects centuries of Irish phonetic adaptation.
Siobhan has been used in Ireland for over five centuries. In English-speaking countries outside Ireland, the unfamiliar spelling-to-sound mapping (Siobhán → shih-VAWN) has limited its use, but it is rising. The actress Siobhan Fallon Hogan and the journalist Siobhan O'Connor are prominent bearers.
Siobhan reduces to five — the number of grace in motion.