WordWeb Online

1. Gain heat or get hot
   "The room heated up quickly";
   - heat, hot up [Brit, informal]
    
2. Make hot or hotter
   "the sun heats up the oceans";
   - heat
    
3. Make more intense
   "Emotions were heated up";
   - hot up [Brit, informal], screw up [informal]

Derived forms: heated up, heats up, heating up

Type of: alter, change, change state, compound, deepen, heighten, intensify, modify, turn