The term 'ingredient in plastics' can be summarized by the crossword solution 'RESIN, ' which is a natural or synthetic compound used as an essential component in the production of plastics. RESIN is a sticky, viscous material that is often used to bind together other materials, such as wood, and is also used in the manufacture of paints, varnishes, and adhesives. RESIN is a versatile material that can be used in a variety of applications, from automotive parts to medical devices.