n. an anticonvulsant barbiturate used for treatment of generalized tonic–clonic or partial seizures. At one time widely used as a sedative and hypnotic, it has been largely supplanted for these purposes by safer medications lacking the toxicity and adverse effects associated with barbiturates. Phenobarbital is also sometimes used in the management of sedative, hypnotic, or anxiolytic withdrawal. U.S. trade name: Luminal.