Santa Soiler is a term used to describe someone who ruins the surprise of Santa Claus for children. The crossword solution for this term is SOOT, which is a black or dark gray powdery or flaky substance made up of carbon particles. It is produced by the incomplete burning of coal, oil, wood, and other organic materials. SOOT is often found in chimneys and is associated with Santa Claus due to the popular image of him coming down the chimney on Christmas Eve.