calm, peaceful, serene, healthy
宁 centers on a state of undisturbed ease: calm, peaceful, and serene. The healthy sense extends this idea to a body or mind free from disturbance.
宁 combines 宀 (roof) with 丁, which may have originally depicted a nail or a person, suggesting stability under a roof. The exact historical development is uncertain, but the idea of calm shelter is consistent.
Under a roof (宀), a nail (丁) is firmly set, creating a stable and peaceful space. Everything is calm and serene.
For チョ, imagine a calm person named Cho sitting peacefully under the roof: Cho -> チョ, and the scene is perfectly serene.