The DICT Development Group

  tranquillise
      v 1: make calm or still; "quiet the dragons of worry and fear"
           [syn: calm, calm down, quiet, tranquilize,
           tranquillize, tranquillise, quieten, lull, still]
           [ant: agitate, charge, charge up, commove,
           excite, rouse, turn on]
      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, tranquillize,
         tranquillise] [ant: arouse, brace, energise,
         energize, perk up, stimulate]