unflurried, reasonable, low, measured, fluid, fair, lenient, noneffervescent, equable, self-possessed, sober, pleasing, stilly, hushed, agreeable, restful, smooth, soundless, comforting, silent, balmy, politic, unperturbed, amicable, sedative, unagitated, angry, suave, liquid, fluent, whispering, even, tame, unflustered, bland, good-tempered, perturbed, legato, muted, agitated, paradisiacal, patient
moderate (part of speech: adjective)
calm (part of speech: adjective)
motionless (part of speech: adjective)
peaceful (part of speech: adjective)
unexcitable (part of speech: adjective)
imperturbable, nonchalant, mild, poker-faced, frigid, demure, passionless, dispassionate, detached, stoic, inscrutable, impassive, controlled, reserved, stoical, stolid, level-headed, placid, aloof, meek, apathetic, self-controlled, self-composed, serene, staid, neutral, steady, easygoing, unflappable, unexcitable, deadpan, even-tempered, numb, unhurried, cold-blooded
- Keep tranquil and cool, Lottie's around!" - "Wives and Widows; or The Broken Life", Ann S. Stephens.
- Fortunately the bed was a good one, and as I had expected it to be uncomfortable I went to sleep in a more tranquil humour. - "The Memoires of Casanova, Complete The Rare Unabridged London Edition Of 1894, plus An Unpublished Chapter of History, By Arthur Symons", Jacques Casanova de Seingalt.
- " Citizen Manette, be tranquil. - "A Tale of Two Cities A Story of the French Revolution", Charles Dickens.