S1E1R1E1N1E1
6 points
SERENE is validvalid
tranquil [adj SERENER, SERENEST] : SERENELY [adv], SERENENESS [n], SERENITY [n] / something that is serene [n SERENES]
calm, tranquil [adj SERENER, SERENEST, SERENELY] / to tranquillize [v SERENED, SERENING, SERENES]