Source : Webster's Revised Unabridged Dictionary (1913)

Sedative \Sed"a*tive\, a. [Cf. F. s['e]datif.]
   Tending to calm, moderate, or tranquilize; specifically
   (Med.), allaying irritability and irritation; assuaging pain.

Sedative \Sed"a*tive\, n. (Med.)
   A remedy which allays irritability and irritation, and
   irritative activity or pain.

Source : WordNet®

sedative
     n : a drug that reduces excitability and calms a person [syn: {sedative
         drug}, {depressant}, {downer}]

sedative
     adj : tending to soothe or tranquilize; "valium has a
           tranquilizing effect"; "took a hot drink with sedative
           properties before going to bed" [syn: {ataractic}, {ataraxic},
            {tranquilizing}, {tranquilising}]