PLAC'ID, adjective [Latin 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.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI