Chimney grime is a combination of SOOT and other particles that accumulate in chimneys over time. SOOT, which is the four-letter answer to this crossword puzzle, is a black or dark gray powdery or flaky substance made up of carbon particles that are released into the air when something is burned. Chimney grime is created when SOOT and other particles settle on the walls of the chimney and accumulate over time.