Source : Webster's Revised Unabridged Dictionary (1913)

Pneumatics \Pneu*mat"ics\, n. [Cf. F. pneumatique.]
   1. That branch of science which treats of the mechanical
      properties of air and other elastic fluids, as of their
      weight, pressure, elasticity, etc. See {Mechanics}.

   2. (Philos. & Theol.) The scientific study or knowledge of
      spiritual beings and their relations to God, angels, and
      men.

Source : WordNet®

pneumatics
     n : the branch of mechanics that deals with the mechanical
         properties of gases