The term "ass a sling" may be a colloquialism and is not a widely recognized term. However, if we are to consider alternative synonyms for the word "ass," we can consider the words "donkey," "mule," and "burro." Additionally, there are countless slang terms for the word "ass," such as "booty," "behind," "bum," or "butt." It is important to note that some of these terms may be considered vulgar or offensive in certain contexts, so they should be used with discretion. Overall, there are many ways to refer to the posterior, and it is up to the speaker to determine the most appropriate term for the given situation.