Foul matter is a term used to describe any type of dirt, debris, or other undesirable substances. The two crossword solutions for this term are FILTH (5 letters) and SCUM (4 letters). FILTH is a term used to describe any type of dirt, grime, or other unpleasant material, while SCUM is a term used to describe a thin layer of impure or unclean material that forms on the surface of a liquid. Both terms are often used to describe the same type of material, but FILTH is generally considered to be more offensive than SCUM.