heat up
phrasal verb
heated up;
heating up;
heats up
Definition of heat up
1
: to become warm or hot
The morning started out cold but it heated up quickly.
2
: to become more active, intense, or angry
Their conversation started to heat up. Competition between the two companies is heating up.
3
heat (something) up
or heat up (something)
: to cause (something) to become warm or hot
Could you heat up the vegetables, please?