Source : Webster's Revised Unabridged Dictionary (1913)

Opiate \O"pi*ate\, n. [From {Opium}: cf.F. opiat.]
   1. Originally, a medicine of a thicker consistence than
      sirup, prepared with opium. --Parr.

   2. Any medicine that contains opium, and has the quality of
      inducing sleep or repose; a narcotic.

   3. Anything which induces rest or inaction; that which quiets
      uneasiness.

            They chose atheism as an opiate.      --Bentley.

Opiate \O"pi*ate\, a. [See {Opium}.]
   Inducing sleep; somniferous; narcotic; hence, anodyne;
   causing rest, dullness, or inaction; as, the opiate rod of
   Hermes. --Milton.

Opiate \O"pi*ate\, v. t.
   To subject to the influence of an opiate; to put to sleep.
   [R.] --Fenton.

Source : WordNet®

opiate
     n : a narcotic drug that contains opium or an opium derivative