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

1) peaceful, tranquil, calm, pacific, peaceable, restful, halcyon, idyllic, bucolic, pastoral, undisturbed, unruffled, imperturbable, unperturbed, untroubled, quiet, still: With the turmoil of the love affair behind her, Sharon looked ahead to a more serene life. 2) calm, cool, collected, placid, composed, self-possessed, poised, unexcitable, even-tempered, temperate, nonchalant, easygoing, cool-headed, easy, Colloq unflappable: Beneath William's serene exterior lay a seething, churning miasma of violent lust.