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.
German: from Middle High German kīl ‘wedge’, ‘wooden peg’, hence possibly a metonymic occupational name for a maker of such pegs or for a wood chopper. Alternatively, it may be nickname for an uncouth or misshapen person (compare Keidel) or a topographic name for someone who lived on or near a wedgeshaped plot of land.