The antonyms for the word "air cool" are hot, warm, sultry, stifling, muggy, and sweltering. While air cool suggests a refreshing and chill temperature, hot and warm imply heat and discomfort. Sultry refers to a humid and oppressive weather condition, while stifling and muggy denote lack of ventilation and discomfort in breathing. Sweltering is a term used to describe extremely hot weather conditions, often characterized by high humidity levels. Hence, these antonyms highlight the opposite of air cool and are used to describe different weather conditions that can affect one's physical and mental state.