The phrase "not for a/one moment" is often used to indicate an absolute refusal or rejection of an idea or proposal. There are several synonyms that convey a similar sentiment, including "under no circumstances," "absolutely not," "never," "not at all," "not in the slightest," and "not for a second." These phrases emphasize the speaker's firm stance and leave no room for negotiation or compromise. They can be useful in situations where a clear and decisive response is necessary, such as in negotiations or when setting boundaries. Using such language can also demonstrate confidence and assertiveness, which can be valuable in many aspects of life.