Found 4 synonyms
tranquillity, serenity, quietness, peacefulness, peace, quietude, repose, placidity, restfulness, slowness.
equanimity, coolness, imperturbability, cool head.
quiet, cool, silence.
calm sea (noun)
More calmness synonyms
peace of mind, quiescence, doldrums,
Synonyms "calmness" in the picture