FLUE GRIME is a combination of two words that refer to a type of dirt or dust that accumulates in chimneys and other areas where smoke is present. The first word, FLUE, is a four-letter word meaning a duct or passage for smoke in a chimney. The second word, GRIME, is also a four-letter word meaning a black or dark-colored deposit of dirt or SOOT. Together, FLUE GRIME refers to the accumulation of SOOT and dirt that builds up in chimneys and other areas where smoke is present.