The phrase "in perpetuity" is often used to describe something that is meant to last forever. Synonyms for this expression could include phrases such as "eternally," "forevermore," or "for all time." Other synonyms might include words like "permanently," "endlessly," or "unendingly." Still others might use phrases like "for all eternity," "unceasingly," or "infinitely." Regardless of the terminology, the concept remains the same, and it is one that speaks to the endurance of something over time, suggesting that it will last forever, without end. Whether referring to relationships, contracts, or other arrangements, using one of these synonyms can help to express the idea of something that will endure over the long term, no matter what.