Antonyms for the phrase "haddest a fit" include calmness, composure, tranquility, serenity, poise, balance, and stability. These words describe a state of being that is opposite to the intense emotional outburst or tantrum implied by the original phrase. When one is calm, they are in control of their emotions and can handle situations in a rational way without losing their cool. Composure refers to the ability to remain calm and collected, even in stressful or challenging situations, while tranquility and serenity describe a peaceful and relaxed state of mind. Poise, balance, and stability all suggest a sense of equilibrium and control, even in the face of adversity.