The Collaborative International Dictionary of English v.0.48:

crowded \crowded\ adj.
   1. overfilled or compacted or concentrated; filled to excess;
      as, a crowded program. Opposite of uncrowded.

   Note: [Narrower terms: full, jammed, jam-packed, packed]
         [WordNet 1.5]

   2. filled with a crowd; as, a crowded marketplace.
      [PJC]

   3. having an uncomfortable density of people; filled to
      excess with people; as, crowded trains; a crowded theater.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Crowd \Crowd\ (kroud), v. t. [imp. & p. p. Crowded; p. pr. &
   vb. n. Crowding.] [OE. crouden, cruden, AS. cr[=u]dan; cf.
   D. kruijen to push in a wheelbarrow.]
   1. To push, to press, to shove. --Chaucer.
      [1913 Webster]

   2. To press or drive together; to mass together. "Crowd us
      and crush us." --Shak.
      [1913 Webster]

   3. To fill by pressing or thronging together; hence, to
      encumber by excess of numbers or quantity.
      [1913 Webster]

            The balconies and verandas were crowded with
            spectators, anxious to behold their future
            sovereign.                            --Prescott.
      [1913 Webster]

   4. To press by solicitation; to urge; to dun; hence, to treat
      discourteously or unreasonably. [Colloq.]
      [1913 Webster]

   To crowd out, to press out; specifically, to prevent the
      publication of; as, the press of other matter crowded out
      the article.

   To crowd sail (Naut.), to carry an extraordinary amount of
      sail, with a view to accelerate the speed of a vessel; to
      carry a press of sail.
      [1913 Webster]

WordNet (r) 3.0 (2006):

crowded
    adj 1: overfilled or compacted or concentrated; "a crowded
           theater"; "a crowded program"; "crowded trains"; "a young
           mother's crowded days" [ant: uncrowded]

Moby Thesaurus II by Grady Ward, 1.0:

135 Moby Thesaurus words for "crowded":
   alive with, angustifoliate, angustirostrate, angustisellate,
   angustiseptal, at the double, awash, bloated, brimful, brimming,
   bristling, bursting, chock-full, choked, circumscribed, close,
   close-fitting, close-knit, close-textured, close-woven, compact,
   compacted, compressed, concentrated, concrete, condensed, confined,
   congested, consolidated, constricted, crammed, crammed full, cramp,
   cramped, crawling, crowding, dense, distended, double-quick,
   double-time, drenched, filled to overflowing, firm, full, gluey,
   glutted, gorged, hard, hard-pressed, hard-pushed, hard-run, heavy,
   hurried, hyperemic, impenetrable, impermeable, in profusion,
   in spate, incapacious, incommodious, isthmian, isthmic, jam-packed,
   jammed, lavish, limited, loaded, massive, meager, narrow, near,
   nonporous, on the double, overblown, overburdened, overcharged,
   overfed, overflowing, overfraught, overfreighted, overfull,
   overladen, overloaded, overstocked, overstuffed, oversupplied,
   overweighted, packed, plethoric, populous, pressed,
   pressed for time, prodigal, profuse, proliferating, prolific,
   pushed, ready to burst, restricted, rife, running over, rushed,
   satiated, saturated, scant, scanty, serried, slender, soaked,
   solid, strait, studded, stuffed, stuffed up, substantial,
   superabundant, supercharged, supersaturated, surcharged, surfeited,
   swarming, swollen, teeming, thick, thick as hail, thick with,
   thick-coming, thick-growing, thickset, thronged, thronging, tight,
   viscid, viscose, viscous