The antonyms for the word "most hysteric" can be found in words like calm, composed, collected, cool, tranquil, peaceful, serene, unflappable, unruffled, and steady. These words denote a sense of control and level-headedness that is the opposite of hysteria. While hysteria suggests a state of extreme emotions or panic, antonyms like composed or serene imply a state of inner peace and a lack of agitation. So, the next time you encounter someone who seems to be "most hysteric," try to soothe them with some calming words, and remind them that staying composed and tranquil is always better than losing control.