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]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "army":
   KP, a mass of, a world of, armed force, armed service, army group,
   array, battalion, battery, battle group, bevy, brigade, bunch,
   cadre, career soldiers, cloud, cluster, clutter, cohort, cohue,
   colony, column, combat command, combat team, company, corps, covey,
   crowd, crush, deluge, detachment, detail, division, drift, drive,
   drove, field army, field train, fighting machine, file, flight,
   flock, flocks, flood, flying column, forces, galaxy, gam, gang,
   garrison, ground forces, ground troops, hail, heap, herd, hive,
   horde, host, jam, kennel, kitchen police, large amount, legion,
   legions, litter, lots, maniple, many, mass, masses of,
   military establishment, mob, muchness, multitude, nest, numbers,
   occupation force, organization, outfit, pack, panoply, paratroops,
   phalanx, platoon, plurality, pod, posse, press, pride, quantities,
   quite a few, rabble, rank, rank and file, ranks, regiment,
   regular army, regulars, rout, ruck, school, scores, section, shoal,
   ski troops, skulk, sloth, soldiery, spate, squad, squadron,
   standing army, storm troops, swarm, tactical unit, task force,
   the line, the military, throng, tidy sum, train, trip, troop,
   troops, unit, wing, worlds of



Easton's 1897 Bible Dictionary:

Army
   The Israelites marched out of Egypt in military order (Ex.
   13:18, "harnessed;" marg., "five in a rank"). Each tribe formed
   a battalion, with its own banner and leader (Num. 2:2; 10:14).
   In war the army was divided into thousands and hundreds under
   their several captains (Num. 31:14), and also into families
   (Num. 2:34; 2 Chr. 25:5; 26:12). From the time of their entering
   the land of Canaan to the time of the kings, the Israelites made
   little progress in military affairs, although often engaged in
   warfare. The kings introduced the custom of maintaining a
   bodyguard (the Gibborim; i.e., "heroes"), and thus the nucleus
   of a standing army was formed. Saul had an army of 3,000 select
   warriors (1 Sam. 13:2; 14:52; 24:2). David also had a band of
   soldiers around him (1 Sam. 23:13; 25:13). To this band he
   afterwards added the Cherethites and the Pelethites (2 Sam.
   15:18; 20:7). At first the army consisted only of infantry (1
   Sam. 4:10; 15:4), as the use of horses was prohibited (Deut.
   17:16); but chariots and horses were afterwards added (2 Sam.
   8:4; 1 Kings 10:26, 28, 29; 1 Kings 9:19). In 1 Kings 9:22 there
   is given a list of the various gradations of rank held by those
   who composed the army. The equipment and maintenance of the army
   were at the public expense (2 Sam. 17:28, 29; 1 Kings 4:27;
   10:16, 17; Judg. 20:10). At the Exodus the number of males above
   twenty years capable of bearing arms was 600,000 (Ex. 12:37). In
   David's time it mounted to the number of 1,300,000 (2 Sam.
   24:9).