The term 'A CHEMICAL USED TO KILL PESTS' can be summarized by three crossword solutions: reagent, LYE, and ants. Reagent is a seven-letter solution that refers to a substance used in a chemical reaction to detect, measure, or produce other substances. LYE is a three-letter solution that refers to a strong alkaline solution of potassium or sodium hydroxide, commonly used for washing or cleaning. Lastly, ants is a four-letter solution that refers to a type of insect that is often considered a pest and can be killed with certain chemicals.