Self-assured manner is a term used to describe a confident and poised demeanor. There are various synonyms that can be used to describe this behavior. For example, "assuredness" can be used to describe a calm and confident approach to situations. "Poise" can describe a graceful self-assuredness and "confidence" can describe a certain level of belief in oneself. Another synonym is "certainty", which suggests a strong conviction in one's ability. Overall, these synonyms highlight the importance of a secure and self-assured demeanor that can lead to success in personal and professional settings.