1. Pert. to sleep or hypnosis. 2. An agent that causes an insensitivity to pain by inhibiting afferent impulses or by inhibiting the reception of sensory impressions in the cortical centers of the brain, thus causing partial or complete unconsciousness.Hypnotics include sedatives, analgesics, anesthetics, and intoxicants, and are sometimes called somnifacients and soporifics when used to induce sleep