Peaceful, a. — Webster enters it under “peaceful”
1. Possessing or enjoying peace; not disturbed by war, tumult, agitation, anxiety, or commotion; quiet; tranquil; as, a peaceful time; a peaceful country; a peaceful end.
2. Not disposed or tending to war, tumult or agitation; pacific; mild; calm; peaceable; as, peaceful words.
Syn. -- See Peaceable. --Peace"ful*ly, adv.. -- Peace"ful*ness, n.
Shades of meaning
Fernald has no entry of its own for peacefulness; he lists it under rest.
He lists it without comment; the entries above explain its neighbors.