1. (adj)sedative, sedative drug, depressant, downer a drug that reduces excitability and calms a person
2. (adj)ataractic, ataraxic, sedative, tranquilizing, tranquillizing, tranquilising, tranquillising tending to soothe or tranquilize "valium has a tranquilizing effect"; "took a hot drink with sedative properties before going to bed"