Source : Webster's Revised Unabridged Dictionary (1913)

Countermarch \Coun"ter*march`\ (koun"t?r-m?rch`), n.
   1. A marching back; retrocession.

   2. (Mil.) An evolution by which a body of troops change front
      or reverse the direction of march while retaining the same
      men in the front rank; also, a movement by which the rear
      rank becomes the front one, either with or without
      changing the right to the left.

   3. A change of measures; alteration of conduct.

            Such countermarches and retractions as we do not
            willingly impute to wisdom.           --T. Burnet.

Countermarch \Coun`ter*march"\ (koun`t?r-m?rch"), v. i. [imp. &
   p. p. {Countermarched} (-m?rcht"); p. pr. & vb. n.
   {Countermarching}.] (Mil.)
   To march back, or to march in reversed order.

         The two armies marched and countermarched, drew near
         and receded.                             --Macaulay.

Source : WordNet®

countermarch
     n : (military) a march in the reverse direction or back along
         the same route
     v 1: march back along the same way
     2: change the order of soldiers during a march