Soporific

Sop′o‐rif″ic (?; 277), a. [L. sopor a heavy sleep (akin to somnus sleep) + facere to make. See Somnolent, Fact.] Causing sleep; tending to cause sleep; soporiferous; as, the soporific virtues of opium.

Syn. — Somniferous; narcotic; opiate; anodyne.