Anglicized spelling of Síle, the Irish Gaelic form of Cecily. This name has become so common and widespread that it is hardly felt to be Irish any longer. In Australia since the 19th century it has been a slang generic term for any woman.
Southern Italian: 1. according to Caracausi, this is from iacono, southern dialect form of diacono ‘deacon’, hence an occupational name for someone in the service of a deacon or a nickname for someone thought to resemble a deacon. 2. Possibly from an augmentative of Giacco, a short form of the personal name Giacomo.