WordWeb Online

1. Make more cheerful
   - lighten, buoy up
    
2. Become more cheerful
   "after a glass of wine, he lightened up a bit";
   - lighten, buoy up
    
3. Make lighter or brighter
   "The paint will lighten up the room";
   - brighten, lighten
    
4. Become lighter
   "The room lightened up";
   - lighten

Derived forms: lightened up, lightens up, lightening up

Type of: alter, change, cheer, cheer up, chirk up, modify