serene

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Content or composed; untroubled.
• adjective Unaffected by disturbance; calm or peaceful: synonym: calm.
• adjective Unclouded; fair.
• adjective Used as a title and form of address for certain members of royalty.

from The Century Dictionary.

• noun The chilly damp of evening; unwholesome air; blight.
• To make clear and calm; tranquilize.
• To clear; clarify.
• Clear, or fair, and calm.
• Calm; placid; unruffled; undisturbed: as, a serene aspect; a serene soul.
• An epithet or adjunct to the titles of some persons of very high rank; it is not given to any noble or official in England, and is used chiefly (in the phrase Serene Highness) in rendering the German term Durchlaucht (given to members of certain mediatized houses, and to some other princes) and the French epithet sérénissime.
• Synonyms 1. Bright, peaceful.—1 and 2. Tranquil, Placid, etc. See calm.—2. Sedate.
• noun Clearness; serenity; a serene expanse or region.
• noun Serenity; placidity; tranquillity; calmness.

from the GNU version of the Collaborative International Dictionary of English.

• noun Poetic. Serenity; clearness; calmness.
• noun obsolete Evening air; night chill.
• transitive verb To make serene.
• adjective Bright; clear; unabscured.
• adjective Calm; placid; undisturbed; unruffled.
• adjective (Med.) See Amaurosis.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A fine rain from a cloudless sky after sunset.
• adjective Peaceful, calm, unruffled.
• adjective without worry or anxiety; unaffected by disturbance.
• adjective archaic (Of the sky) fair and unclouded.
• adjective Used as part of certain titles.
• verb transitive To make serene.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective completely clear and fine
• adjective not agitated; without losing self-possession