Erin is a Hiberno-English derivative of the Irish word "Éirinn". "Éirinn" is the dative case of the Irish word for Ireland - "Éire", genitive "Éireann", the dative being used in prepositional phrases such as "go hÉirinn" "to Ireland", "in Éirinn" "in Ireland", "ó Éirinn" "FROM IRELAND". The dative has replaced the nominative in a few regional Irish dialects (particularly Galway-Connamara and Waterford).