tranquilize in WordNet English dictionary

1. cause to be calm or quiet as by administering a sedative to
   "The patient must be sedated before the operation"
   sedate  calm  tranquilize  tranquillize  tranquillise 
   
2. make calm or still
   "quiet the dragons of worry and fear"
   calm  calm down  quiet  tranquilize  tranquillize  tranquillise  quieten  lull  still