The word “tension” typically doesn't have a past tense form in the traditional sense. However, if we're looking for words that could convey a past state related to tension, here are some options and an analysis:
relieved strain: When tension is released or eased, we can use “relieved strain”. For example, “After the negotiation, there was a sense of relieved strain as the conflict was resolved.” This implies that the previous tension or strain has been alleviated.
eased stress: “Stress” is often associated with tension. If the tension has decreased in the past, we can say “eased stress”. For instance, “The vacation brought an end to months of eased stress.” This shows that there was a prior state of stress or tension that has now been lessened.
dissipated pressure: “Pressure” can also create tension. When that pressure is gone or reduced, we can use “dissipated pressure”. For example, “The team's victory dissipated the pressure that had been building up for weeks.” This indicates that the previous pressure and resulting tension have dissipated.
subsided unease: “Unease” can be a form of tension. If the unease has lessened or gone away in the past, we can say “subsided unease”. For instance, “As the news spread, the subsided unease was replaced by relief.” This shows that there was a prior state of unease or tension that has now subsided.
In conclusion, while there aren't direct past tense synonyms for “tension”, these phrases can help describe a past state where tension has been reduced or eliminated.