The Oxford Thesaurus An A-Z Dictionary of Synonyms - serenityn.

1) peacefulness, peace, tranquillity, calm, calmness, restfulness, quiet, stillness: The serenity of the warm summer's evening was shattered by an enormous explosion. 2) tranquillity, peacefulness, peaceableness, unexcitability, calmness, calm, composure, self-possession, poise, aplomb, even-temperedness, temperance, nonchalance, cool-headedness, placidity, Colloq unflappability: The serenity of her nature was like a safe harbour to the friends who sought comfort from the turbulence of their lives.