The phrase "most sewed-up" typically means something that is secure and certain. Therefore, antonyms for this phrase would be words that convey the opposite meaning, such as "uncertain," "unreliable," "insecure," or "open-ended." These terms imply that there is a lack of assurance or guarantee, which can cause anxiety or doubts. For example, a financial investment that is deemed secure and dependable may have an antonym that is categorized as unpredictable or a high-risk investment. Overall, the antonyms for "most sewed-up" encompass a range of words that describe situations or circumstances that lack confidence, stability, or security.