A viscid substance is a type of material that is thick and sticky. The term can refer to a variety of substances, including GUM (3 letters), gluten (6 letters), ectoplasm (9 letters), and GOO (3 letters). GUM is a type of sticky substance made from tree sap or synthetic materials. Gluten is a protein found in wheat, rye, and barley. Ectoplasm is a mysterious substance associated with spiritualism and the paranormal. GOO is a slang term for any thick, slimy substance.