The word "un tightening" can be replaced with a variety of synonyms, including loosening, slackening, relaxing, easing, and untangling. These words refer to the act of making something less tight, binding, or constricting. They can be used in a variety of contexts, from physical movements and adjustments to emotional or mental states. For example, you might use "loosening" to describe the process of untying a knot, "slackening" to describe a decrease in tension or pressure, or "relaxing" to describe a release of stress or anxiety. Whatever the context, these synonyms all capture the idea of making something less tight or restrictive.