The Collaborative International Dictionary of English v.0.48:

Army \Ar"my\, n. [F. arm['e]e, fr. L. armata, fem. of armatus,
   p. p. of armare to arm. Cf. Armada.]
   1. A collection or body of men armed for war, esp. one
      organized in companies, battalions, regiments, brigades,
      and divisions, under proper officers.
      [1913 Webster]

   2. A body of persons organized for the advancement of a
      cause; as, the Blue Ribbon Army.
      [1913 Webster]

   3. A great number; a vast multitude; a host.
      [1913 Webster]

            An army of good words.                --Shak.
      [1913 Webster]

   Standing army, a permanent army of professional soldiers,
      as distinguished from militia or volunteers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

army
    n 1: a permanent organization of the military land forces of a
         nation or state [syn: army, regular army, ground
         forces]
    2: a large number of people united for some specific purpose
    3: the army of the United States of America; the agency that
       organizes and trains soldiers for land warfare [syn: United
       States Army, US Army, U. S. Army, Army, USA]