Calm

Synonyms: Windless, tranquil, serene, pacific, restful, halcyon, still, quiet, peaceful, undisturbed, and balmy.

Synonyms: Tranquil, like a millpond, glassy, motionless, unagitated, stilly, still, smooth, flat, waveless, and storm-free.

Synonyms: Composure, calmness, sangfroid, poise, self-control, tranquillity, imperturbability, placidness, impassiveness, dispassion, stolidity, unflappability, ataraxia, coolness, self-possession, presence of mind, aplomb, serenity, equanimity, equability, placidity, impassivity, phlegm, cool, and ataraxy.

Synonyms: Tranquillity, calmness, quietness, peace, serenity, hush, repose, stillness, quiet, quietude, peacefulness, silence, and restfulness.

Synonyms: Soothe, placate, appease, hush, gentle, quell, alleviate, quieten (down), dulcify, pacify, mollify, conciliate, lull, tranquillize, allay, assuage, and square off.

Synonyms: Compose oneself, control oneself, keep one's head, cool down, take it easy, get a grip, play it cool, wind down, chill out, stay loose, recover/regain one's composure, pull oneself together, simmer down, cool off, quieten down, keep one's cool, keep one's shirt on, come back down to earth, hang loose, and decompress.