When it comes to antonyms for the phrase "thrashing out," there are several options. One could use words like "agreeing," "cooperating," or "compromising" to convey the opposite meaning. These terms suggest a more collaborative approach to resolving a problem or issue, in contrast to the confrontational tone of "thrashing out." Another possibility is to use the word "ignoring," which implies that the issue in question is not worth addressing or that it can be safely overlooked. In any case, choosing the right antonym will depend on the context and the desired tone of the communication in question.