"No fooling" is a phrase used to emphasize the truthfulness of a statement or the seriousness of a situation. There are several synonyms that can be used in place of "no fooling" depending on the context of the conversation. For example, "seriously," "honestly," and "truthfully" are all synonyms that can be used to convey the same message. Other options include "no joking," "without a doubt," and "in all seriousness." Using these synonyms can add variation to your communication and make your message more impactful. So, whether you're having a serious conversation or want to emphasize the truthfulness of your statement, using synonyms for "no fooling" can help convey your message more effectively.