The Collaborative International Dictionary of English v.0.48:

Osmic \Os"mic\, a. (Chem.)
   Pertaining to, derived from, or containing, osmium;
   specifically, designating those compounds in which it has a
   valence higher than in other lower compounds; as, osmic
   oxide.
   [1913 Webster]

   Osmic acid. (Chem.)
   (a) Osmic tetroxide. [Obs.]
   (b) Osmic acid proper, an acid analogous to sulphuric acid,
       not known in the free state, but forming a well-known and
       stable series of salts (osmates), which were formerly
       improperly called osmites.

   Osmic tetroxide (Chem.), a white volatile crystalline
      substance, OsO4, the most stable and characteristic of
      the compounds of osmium. It has a burning taste, and gives
      off a vapor, which is a powerful irritant poison,
      violently attacking the eyes, and emitting a strong
      chlorinelike odor. Formerly improperly called osmic
      acid.
      [1913 Webster]