"Un-stinging" is a strange and uncommon word, but it does have a few synonyms that can be used to convey a similar meaning. One possible synonym is "soothing", which suggests a calming or relieving effect on the body or mind. Another synonym could be "nonirritating", indicating that a substance or action does not cause irritation or discomfort. "Gentle" is also a common synonym of "un-stinging", denoting something that is soft, mild, and not aggressive. Finally, "nonthreatening" is another option, implying that a situation or condition is not harmful or intimidating. All of these synonyms can be used in different contexts to describe something that is not painful or unpleasant.