Prepare for exercise or an athletic event by stretching or practicing beforehand, as in It's important to warm up before you play any sport. The idiom is also applied to musicians getting ready to perform. [Late 1800s]
Make enthusiastic, excited, or animated, as in He was good at warming up an audience for the main speaker. [Mid-1800s]
warm up to. Become friendlier or more receptive toward, as in I had a hard time warming up to my mother-in-law. [Early 1800s]
Reach a temperature high enough to work efficiently, as in I'll go out and warm up the car. [Mid-1900s]
Reheat food, as in If we warm up the leftovers, we'll have enough for everyone. [Mid-1800s]
Approach a state of violence or confrontation, as in Racial tension was rapidly warming up. Also see heat up.