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 more cheerful through the use of colour
   "The paint will lighten up the room";
   - brighten, lighten
    
4. Become lighter
   "The room lightened up";
   - lighten

Derived forms: lightening up, lightened up, lightens up

Type of: alter, buck up [informal], change, cheer, cheer up, jolly [informal], modify