The Collaborative International Dictionary of English v.0.48:

Officinal \Of*fic"i*nal\, a. [F., fr. L. officina a workshop,
   contr. fr. opificina, fr. opifex a workman; opus work +
   facere to make or do.]
   1. Used in a shop, or belonging to it. [Obs. or R.]
      --Johnson.
      [1913 Webster]

   2. (Pharm.) Kept in stock by apothecaries; -- said of such
      drugs and medicines as may be obtained without special
      preparation or compounding; not magistral.
      [1913 Webster]

   Note: This term is often interchanged with official, but in
         strict use officinal drugs are not necessarily
         official. See Official, a., 3.
         [1913 Webster]