Phlegmaticness is a noun that refers to a state of being calm, composed, and unemotional. There are several synonyms for this word, such as serenity, equanimity, imperturbability, stoicism, and composure. Serenity pertains to a peaceful state of mind and body, while equanimity implies an evenness of temper and character. Imperturbability refers to the ability to remain calm under stress, while stoicism is the quality of enduring pain or hardship without complaint. Composure is the state of being calm and collected, especially in difficult situations. All these synonyms describe a state of mind that is characterized by tranquility, steadiness, and self-possession.