When we say a person or thing is most bristling, we mean that they are filled with tension, anger, or unease. Antonyms for this phrase would describe a state of peace or calmness. Some possible antonyms include serene, tranquil, relaxed, easygoing, composed, or even lukewarm. A serene person, for instance, is someone who is undisturbed and at peace. A tranquil scene is free from disturbance or agitation. A relaxed atmosphere is one that is casual and laid-back. These antonyms can help us understand the opposite of most bristling and imagine a more peaceful state of mind.