Sang-froid is the power to stay calm and clear-headed when something is dangerous, embarrassing, or about to go wrong — not the kind of courage that charges forward, but a cool, almost cold, steadiness. English borrowed it from French, and it still feels formal and a little literary: you use it in careful writing or a story, not when chatting with friends (they would say she kept her cool). It is usually slightly admiring. Though actually, it can also sound a bit chilly, as if the person feels too little; that depends on the writer's tone. It has nothing to do with singing, even though sang looks like the past of sing.

沉著、處變不驚（文雅）