soporiferous

from WordNet (r) 3.0 (2006)

soporiferous
    adj 1: sleep inducing [syn: {soporific}, {soporiferous},
           {somniferous}, {somnific}, {hypnogogic}, {hypnagogic}]
    2: inducing mental lethargy; "a narcotic speech" [syn:
       {narcotic}, {soporiferous}, {soporific}]

from The Collaborative International Dictionary of English v.0.48

Soporiferous \Sop`o*rif"er*ous\, a. [L. soparifer; sopor a heavy
   sleep + ferere to bring.]
   Causing sleep; somniferous; soporific. "Soporiferous
   medicine." --Swift.
   [1913 Webster] -- {Sop`o*rif"er*ous*ly}, adv. --
   {Sop`o*rif"er*ous*ness}, n.
   [1913 Webster]