The phrase "cold sheet" can refer to a number of different things, depending on the context. Some possible synonyms for this term might include words like "chilled bed linen," "frosty bedclothes," or "icy covers." Alternatively, if someone is accused of being a "cold sheet" in the sense of being emotionally distant or unresponsive, you might use words like "detached," "unfeeling," or "unresponsive" to describe their demeanor. In a medical or scientific context, "cold sheet therapy" is sometimes used to describe a treatment where a patient's body is cooled to help treat conditions like fever or heatstroke. In this sense, you could use words like "hypothermia treatment" or "cool therapy" to describe the same process.