For a sigh of relief:
* "Ahhh" - This is the most common and straightforward option, representing a deep exhale of release.
* "Whew" - This suggests a more intense release of tension, perhaps after a close call.
* "Phew" - Similar to "whew," but perhaps slightly less dramatic.
Other options:
* "Thump" - Could represent a sudden feeling of relaxation, as if a weight has been lifted.
* "Click" - Could suggest a mental "switch" being flipped from anxiety to relief.
* "Gulp" - Could indicate a moment of relief after overcoming a stressful situation.
Ultimately, the best onomatopoeic word for expressing relief will depend on the context and the desired effect.