How does Cicero refer to "peace of mind"?

Cicero uses the term "tranquillitas" to refer specifically to "peace of mind." This word encapsulates a state of calmness and serenity, indicating a sense of inner peace and stability amidst life’s challenges. In Cicero's writings, “tranquillitas” conveys not only the absence of disturbance but also a deeper philosophical sense of being unshaken by external circumstances—a quality that is highly valued in Stoic thought, which Cicero often engages with in his works.

While "serenity," "equanimity," and "calmness" also capture aspects of peace of mind, they do not have the same direct connection to Cicero's terminology or his philosophical context. "Serenity" usually refers to a peaceful state, but it is more generic. "Equanimity" is more about mental stability especially in difficult situations, and "calmness" indicates a lack of agitation but lacks the deeper philosophical undertones that "tranquillitas" provides in Cicero’s discourse on the virtues of a wise life. Therefore, "tranquillitas" is the most accurate reflection of Cicero's expression of "peace of mind."