The term WARM UP, AS FOOD can be solved by two crossword solutions: HEAT (4 letters) and REHEAT (6 letters). HEAT is a verb that means to raise the temperature of something, usually through the application of HEAT. Reheat is a verb that means to HEAT something that has already been cooked or heated before. Both terms are commonly used when referring to food, as it is necessary to HEAT food in order to make it safe to eat.