placid

even, even-keeled, steady, well-adjusted, well-balanced

imperturbable, nerveless, unflappable, unshakable

centered, disciplined, equable, self-contained, self-controlled

affable, breezy, devil-may-care, easygoing, happy-go-lucky, laid-back, loosey-goosey, mellow

carefree, nonchalant, unconcerned

assured, confident, self-assured

aloof, detached, dispassionate, indifferent

bovine, impassive, phlegmatic, sober, stolid

relaxed, relieved, tranquilized (also tranquillized)

balmy, clement, equable, gentle, mild, moderate, temperate

clear, cloudless, fair, rainless, sunny, sunshiny, windless

noiseless, silent, soundless

mute, speechless, wordless

dead, motionless, quiescent

muffled, muted, quieted

dull, gentle, low, soft

ultraquiet