Retroaction is a term commonly used in physics and engineering to describe the feedback or reaction that occurs as a result of a system's behavior or performance. However, there are several synonyms that can be used in place of retroaction depending on the context of the discussion. Synonyms for retroaction include feedback, reaction, response, repercussion, consequence, and effect. Each of these synonyms can be used to describe the same concept of cause and effect, but they may have slightly different connotations or nuances. It's important to choose the appropriate synonym depending on the specific application or context where it will be used.