PLAC'ID, a. [L. placidus, from placo, to appease.]
1. Gentle; quiet; undisturbed; equable; as a placid motion of the spirits.2. Serene; mild; unruffled; indicating peace of mind; as a placid countenance or smile.3. Calm; tranquil; serene; not stormy; as a placid sky.4. Calm; quiet; unruffled; as a placid stream.