From Greek 'kauma' (burning heat) via Latin and Italian — named for the midday stillness when the sun halted all activity.
Not showing or feeling nervousness, anger, or other strong emotions; peaceful and still.
From Old French 'calme,' from Italian 'calma,' from Late Latin 'cauma' meaning 'heat of the midday sun,' from Greek 'kauma' (burning heat). The logic: during midday heat, all activity stops — hence stillness. Key roots: kauma (Greek: "burning heat").