Calm and collected; composed and level-headed—able to deal with situations without panic, commonly used in everyday speech.
彼は緊急時でも沈着冷静に状況を分析した。
Even in an emergency he calmly analyzed the situation.
面接では沈着冷静に受け答えすることが大切だ。
In interviews it's important to answer calmly and composedly.
彼女の沈着冷静な態度がチームを落ち着かせた。
Her calm and collected manner steadied the team.
沈着冷静さを失うと、判断を誤りやすくなる。
Losing composure makes it easier to make wrong judgments.