Thrashes out is a term that means to solve or discuss a problem in a detailed and forceful way. When it comes to antonyms, the first word that comes to mind is "ignores." By ignoring a problem, no effort is made to find a solution or to address the issue. Another antonym would be "avoids," as it suggests the act of intentionally evading the discussion or problem at hand. "Postpones" is another word that could be used as its antonym, implying that the issue won't be resolved anytime soon or at this moment. Lastly, "disregards" could be used as antonyms for "thrashes out," it suggests a dismissive attitude towards the problem or discussion.