Restful comes from rest + -ful, the noun rest deriving from Old English ræst ('rest, repose'), from Proto-Germanic *rastō. The suffix is part of the word's derivational shape, marking the final grammatical or semantic role while the base supplies the central meaning. As an adjective, it carries the sense "giving a feeling of peace and relaxation; tranquil", with the older formation still helping explain the modern use. Relevant historical forms include Old English ræst and Proto-Germanic *rastō. Derivative forms include restfully, restfulness; related words include rest, restless, resting.