soporific (adj.)

"tending to produce sleep," 1680s, from French soporifique (17c.), formed in French from Latin sopor (genitive soporis) "deep sleep" (from PIE root *swep- "to sleep"). As a noun from 1722. Earlier as an adjective was soporiferous (1580s as "characterized by excessive sleep," c. 1600 as "soporific").