There are several synonyms for the phrase "not permitted." One common synonym is "prohibited," which means that something is not allowed or banned. Another similar phrase is "forbidden," meaning that an action or thing is not permitted under any circumstances. "Disallow" is another synonym, which means to refuse or reject permission. "Banned," "outlawed," "tabooed," and "restricted" are also synonyms that convey the idea of something not being allowed. In essence, these synonyms all communicate that a particular activity, behavior, or action is not acceptable or sanctioned.