serene in WordNet English dictionary

1. not agitated; without losing self-possession
   "spoke in a calm voice"; "remained calm throughout the uproar"; "he remained serene in the midst of turbulence"; "a serene expression on her face"; "she became more tranquil"; "tranquil life in the country"
   calm  unagitated  serene  tranquil 
   
2. completely clear and fine
   "serene skies and a bright blue sea"
   serene