Retroact refers to an action that is taken or an event that occurs at a time prior to the present. The word has limited synonyms in the English language, with the primary substitute being the word 'retrospect,' which describes looking back on past events. Other alternatives for retroact include 'retrace,' 'revisit,' and 're-examine' since they also imply revisiting events or previous actions. 'Backtrack,' 'recall,' and 'revoke' can also be used in specific contexts to replace retroact. However, it is worth noting that none of these terms precisely conveys the meaning of retroact. Therefore, the word retroact remains the best option when describing something that has happened in the past.