He managed to keep calm and not lose his cool during the crisis.

lose 是动词，意思是"失去、丧失"。 his 是代词 he 的所有格形式，表示"他的"。 cool 在这里是名词，意思是"冷静、镇定"。 lose his cool 是一个固定短语，字面意思是"失去冷静"，引申为"突然发怒、失控"的意思。