Source : Webster's Revised Unabridged Dictionary (1913)

Direct-acting \Di*rect"-act`ing\, a. (Mach.)
   Acting directly, as one part upon another, without the
   intervention of other working parts.

   {Direct-acting steam engine}, one in which motion is
      transmitted to the crank without the intervention of a
      beam or lever; -- also called {direct-action steam
      engine}.

   {Direct-acting steam pump}, one in which the steam piston rod
      is directly connected with the pump rod; -- also called
      {direct-action steam pump}.