tranquillize
     v 1: make calm or still; "quiet the dragons of worry and fear"
          [syn: {calm}, {calm down}, {quiet}, {tranquilize}, {tranquillise},
           {quieten}, {lull}, {still}] [ant: {agitate}]
     2: cause to be calm or quiet as by administering a sedative to;
        "The patient must be sedated before the operation" [syn: {sedate},
         {calm}, {tranquilize}, {tranquillise}] [ant: {stimulate}]
Source: WordNet® 2.0