"Boiling mad" is an expression that describes extreme anger and frustration. However, there are several antonyms for this phrase that convey the opposite meaning. These include "calm," "composed," "collected," "cool," "serene," "placid," "tranquil," "peaceful," "relaxed," "unperturbed," and "zen-like." Use these antonyms to describe a state of tranquillity, poise, and serenity, which highlight someone in control of their emotions. Alternatively, they can serve to describe a situation that lacks heated emotions and conflict. By using these opposite words, you can convey a sense of balance, peace, and composure to your writing.