Merriam-Webster Collegiate Dictionary - serene

 I. adjective  Etymology: Middle English, from Latin serenus clear, cloudless, untroubled  Date: 15th century  1.  a. clear and free of storms or unpleasant change ~ skies  b. shining bright and steady the moon, ~ in glory — Alexander Pope  2. august — used as part of a title His Serene Highness  3. marked by or suggestive of utter calm and unruffled repose or quietude a ~ smile  Synonyms: see calm  • ~ly adverb  • ~ness noun  II. noun  Date: 1644  1. archaic a ~ condition or expanse (as of sky, sea, or light)  2. archaic serenity, tranquility