The phrase "wont wash" is an idiom that means something is not acceptable or believable. Some antonyms for this phrase include "credible," "plausible," "reasonable," "believable," and "convincing." These words refer to something that is regarded as trustworthy, reliable and acceptable. Conversely, antonyms for "wont wash" also include "invalid," "implausible," "unreasonable," "incredible," and "unbelievable." These words describe a situation or argument that lacks credibility or fails to present convincing evidence. By using appropriate antonyms, we can accurately communicate our thoughts and opinions on a subject and convey our stance on whether a situation or idea is likely or unlikely to be factual.