1. To make better
   "The editor ameliorated the manuscript with his changes";
   - better, improve, amend, meliorate, mend
    
2. Get better
   "The weather ameliorated toward evening";
   - better, improve, meliorate

Derived forms: ameliorating, ameliorates, ameliorated

Type of: alter, change, change state, modify, turn

Encyclopedia: Ameliorate