The word 'enduring' refers to something that lasts over time, is long-lasting, or withstands the test of time. The term 'perpetual' captures this essence of continuity and permanence, indicating something that is never-ending or constantly recurring. It suggests an ongoing existence without interruption, closely aligning with the meaning of 'enduring.'
In contrast, terms like 'temporary,' 'fleeting,' and 'brief' imply a lack of longevity. These words suggest that something exists for a short period or is transient, which is the opposite of what 'enduring' conveys. Therefore, 'perpetual' is the most fitting synonym, as it embodies the strength and continuity associated with endurance.