The term COMPOUND USED IN PLASTICS can be summarized by two crossword solutions: POLYMER (7 letters) and UREA (4 letters). Polymers are large molecules composed of repeating structural units, and they are used in a wide variety of products such as plastics, adhesives, and synthetic fibers. Urea is an organic compound made up of carbon, nitrogen, oxygen, and hydrogen atoms. It is used in the production of plastics, fertilizers, and resins.