The Collaborative International Dictionary of English v.0.48:

Opiate \O"pi*ate\, n. [From Opium: cf. F. opiat.]
   1. Originally, a medicine of a thicker consistency than
      sirup, prepared with opium. --Parr.
      [1913 Webster]

   2. Any medicine that contains opium, and has the quality of
      inducing sleep or repose; a narcotic.
      [1913 Webster]

   3. Anything which induces rest or inaction; that which quiets
      uneasiness.
      [1913 Webster]

            They chose atheism as an opiate.      --Bentley.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Opiate \O"pi*ate\, v. t.
   To subject to the influence of an opiate; to put to sleep.
   [R.] --Fenton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

opiate
    n 1: a narcotic drug that contains opium or an opium derivative

The Devil's Dictionary (1881-1906):

OPIATE, n.  An unlocked door in the prison of Identity.  It leads into
the jail yard.