soporific adj.- causing sleep
something that causes sleep
soporific (adj.) “tending to produce sleep,” 1680s, from French soporifique (17c.), formed in French from Latin sopor (genitive soporis) “deep sleep” (see sopor). As a noun from 1722. Earlier as an adjective was soporiferous (1580s as “characterized by excessive sleep,” c.1600 as “soporific”).