The Collaborative International Dictionary of English v.0.48:

Horde \Horde\ (h[=o]rd), n. [F. horde (cf. G. horde), fr. Turk.
   ord[=u], ord[imac], camp; of Tartar origin.]
   1. A wandering troop or gang; especially, a clan or tribe of
      a nomadic people migrating from place to place for the
      sake of pasturage, plunder, etc.; a predatory multitude.
      --Thomson.
      [1913 Webster]

   2. Hence: Any large group of people or animals, especially
      one wandering or moving about; as, the movie star was
      surrounded by a horde of screaming fans.
      [PJC]

WordNet (r) 3.0 (2006):

horde
    n 1: a vast multitude [syn: horde, host, legion]
    2: a nomadic community
    3: a moving crowd [syn: drove, horde, swarm]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "horde":
   army, assemble, bunch, bunch up, clot, cluster, cohue, collect,
   come together, congregate, converge, copulate, couple, crowd,
   crush, date, deluge, drove, flock, flock together, flood,
   flow together, forgather, fuse, galaxy, gang around, gang up,
   gather, gather around, heap, herd together, hive, host, huddle,
   ignobile vulgus, jam, league, legion, link, many-headed multitude,
   mass, meet, merge, mill, mob, mobile vulgus, multitude, muster,
   panoply, press, push, rabble, rally, rally around, rendezvous,
   rout, ruck, seethe, spate, squash, stream, surge, swarm,
   the common herd, the crowd, the great unnumbered,
   the great unwashed, the herd, the hoi polloi, the horde,
   the majority, the many, the masses, the mob, the multitude, throng,
   unite