1. causing or tending to cause sleep.
2. pertaining to or characterized by sleep or sleepiness; sleepy; drowsy.
3. something that causes sleep, as a medicine or drug.
Example: Her doctor prescribed a soporific to help her sleep better.
Origin: 1690, from Fr. soporifique (1687), formed in Fr. from L. sopor (gen. soporis) "deep sleep."