1. Alleviate or remove (pressure or stress) or make less oppressive
   "lighten the burden of caring for her elderly parents";
   - relieve
    
2. Reduce the weight on; make lighter
   "she lightened the load on the tired donkey"
    
3. Become lighter
   "The room lightened up";
   - lighten up
    
4. Make more cheerful
   "the conversation lightened me up a bit";
   - lighten up, buoy up
    
5. Become more cheerful
   "after a glass of wine, he lightened up a bit";
   - lighten up, buoy up
    
6. Make more cheerful through the use of colour
   "The paint will lighten up the room";
   - brighten, lighten up

Derived forms: lightens, lightening, lightened

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

Antonym: darken