NOUN (1)

1. (military) a march in the reverse direction or back along the same route;


VERB (2)

1. march back along the same way;

2. change the order of soldiers during a march;

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         The two armies marched and countermarched, drew near
         and receded.                             --Macaulay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Countermarch \Coun"ter*march`\ (koun"t?r-m?rch`), n.
   1. A marching back; retrocession.
      [1913 Webster]

   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.
      [1913 Webster]

   3. A change of measures; alteration of conduct.
      [1913 Webster]

            Such countermarches and retractions as we do not
            willingly impute to wisdom.           --T. Burnet.
      [1913 Webster]

WordNet (r) 3.0 (2006):

countermarch
    n 1: (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