The Collaborative International Dictionary of English v.0.48:

Multitude \Mul"ti*tude\, n. [F. multitude, L. multitudo,
   multitudinis, fr. multus much, many; of unknown origin.]
   1. A great number of persons collected together; a numerous
      collection of persons; a crowd; an assembly.
      [1913 Webster]

            But when he saw the multitudes, he was moved with
            compassion on them.                   --Matt. ix.
                                                  36.
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   2. A great number of persons or things, regarded
      collectively; as, the book will be read by a multitude of
      people; the multitude of stars; a multitude of cares.
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            It is a fault in a multitude of preachers, that they
            utterly neglect method in their harangues. --I.
                                                  Watts.
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            A multitude of flowers
            As countless as the stars on high.    --Longfellow.
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   3. The state of being many; numerousness.
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            They came as grasshoppers for multitude. --Judg. vi.
                                                  5.
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   The multitude, the populace; the mass of men.
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   Syn: Throng; crowd; assembly; assemblage; commonalty; swarm;
        populace; vulgar. See Throng.
        [1913 Webster]

WordNet (r) 3.0 (2006):

multitude
    n 1: a large indefinite number; "a battalion of ants"; "a
         multitude of TV antennas"; "a plurality of religions" [syn:
         battalion, large number, multitude, plurality,
         pack]
    2: a large gathering of people [syn: multitude, throng,
       concourse]
    3: the common people generally; "separate the warriors from the
       mass"; "power to the people" [syn: multitude, masses,
       mass, hoi polloi, people, the great unwashed]

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "multitude":
   a mass of, a world of, abundance, acres, army, bags, barrels, bevy,
   bunch, bushel, cloud, cluster, clutter, cohue, copiousness,
   countlessness, covey, crowd, crush, deluge, flight, flock, flocks,
   flood, galaxy, hail, heap, hive, horde, host, ignobile vulgus, jam,
   large amount, legion, load, lots, many, many-headed multitude,
   mass, masses of, mob, mobile vulgus, mountain, much, muchness,
   nest, numbers, numerousness, ocean, oceans, pack, panoply, peck,
   plenitude, plenty, plurality, press, profusion, quantities,
   quantity, quite a few, rabble, rout, ruck, scores, sea, shoal,
   spate, superabundance, superfluity, 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, tidy sum, tons, volume, world,
   worlds, worlds of



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MULTITUDE. The meaning of this word is not very certain. By some it is said
that to make a multitude there must be ten persons at least, while others
contend that the law has not fixed any number. Co. Litt. 257.



The Devil's Dictionary (1881-1906):

MULTITUDE, n.  A crowd; the source of political wisdom and virtue.  In
a republic, the object of the statesman's adoration.  "In a multitude
of counsellors there is wisdom," saith the proverb.  If many men of
equal individual wisdom are wiser than any one of them, it must be
that they acquire the excess of wisdom by the mere act of getting
together.  Whence comes it?  Obviously from nowhere -- as well say
that a range of mountains is higher than the single mountains
composing it.  A multitude is as wise as its wisest member if it obey
him; if not, it is no wiser than its most foolish.