Heat up is a common term that can refer to increasing the temperature of something or someone. Some synonyms for heat up include warm up, heat, cook, toast, roast, broil, and bake. These words are often used in cooking, but can also be used to describe the weather or the physical effects of exercise. Additionally, they can be used metaphorically to describe an increase in intensity or tension in a situation or relationship. Using synonyms for heat up can add variety to your writing and help you avoid repeating the same phrase.