The Collaborative International Dictionary of English v.0.48:

Jam \Jam\, v. t. [imp. & p. p. Jammed (j[a^]md); p. pr. & vb.
   n. Jamming.] [Either fr. jamb, as if squeezed between
   jambs, or more likely from the same source as champ See
   Champ.]
   [1913 Webster]
   1. To press into a close or tight position; to crowd; to
      squeeze; to wedge in; to cram; as, rock fans jammed the
      theater for the concert.
      [1913 Webster]

            The ship . . . jammed in between two rocks. --De
                                                  Foe.
      [1913 Webster]

   2. To crush or bruise; as, to jam a finger in the crack of a
      door. [Colloq.]
      [1913 Webster]

   3. (Naut.) To bring (a vessel) so close to the wind that half
      her upper sails are laid aback. --W. C. Russell.
      [1913 Webster]

   4. To block or obstruct by packing too much (people or
      objects) into; as, shoppers jammed the aisles during the
      fire sale.
      [PJC]

   5. (Radio) To interfere with (a radio signal) by sending
      other signals of the same or nearby frequency; as, the
      Soviets jammed Radio Free Europe broadcasts for years
      during the cold war.
      [PJC]

   6. To cause to become nonfunctional by putting something in
      that blocks the movement of a part or parts; as, he jammed
      the drawer by putting in too many loose papers; he jammed
      the lock by trying to pick it.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

jammed \jammed\ adj.
   filled to capacity or overfilled; as, the auditorium was
   jammed to the rafters.

   Syn: full, jam-packed, packed.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

jammed
    adj 1: filled to capacity; "a suitcase jammed with dirty
           clothes"; "stands jam-packed with fans"; "a packed
           theater" [syn: jammed, jam-packed, packed]

Moby Thesaurus II by Grady Ward, 1.0:

163 Moby Thesaurus words for "jammed":
   aground, alive with, anchored, arrested, back, backward,
   behindhand, belated, bloated, blocked, bonded, bound, brimful,
   brimming, bristling, bursting, caught, cemented, chained,
   chock-full, choked, choked up, clogged, clogged up, close,
   close-knit, close-textured, close-woven, compact, compacted,
   compressed, concentrated, concrete, condensed, congested,
   consolidated, constipated, costive, crammed, crammed full,
   crawling, crowded, crowding, delayed, delayed-action, dense,
   detained, distended, drenched, fast, fastened,
   filled to overflowing, firm, fixed, foul, fouled, full, glued,
   gluey, glutted, gorged, grounded, hard, heavy, held, held up,
   high and dry, hung up, hyperemic, impacted, impenetrable,
   impermeable, in a bind, in abeyance, in profusion, in spate,
   inextricable, infarcted, jam-packed, late, latish, lavish, massive,
   moored, moratory, never on time, nonporous, obstipated, obstructed,
   overblown, overburdened, overcharged, overdue, overfed,
   overflowing, overfraught, overfreighted, overfull, overladen,
   overloaded, overstocked, overstuffed, oversupplied, overweighted,
   packed, plethoric, plugged, plugged up, populous, prodigal,
   profuse, proliferating, prolific, ready to burst, retarded, rife,
   running over, satiated, saturated, secure, serried, set, slow,
   soaked, solid, stopped, stopped up, stranded, stuck, stuck fast,
   studded, stuffed, stuffed up, substantial, superabundant,
   supercharged, supersaturated, surcharged, surfeited, swarming,
   swollen, taped, tardy, teeming, tethered, thick, thick as hail,
   thick with, thick-coming, thick-growing, thickset, thronged,
   thronging, tied, tight, transfixed, unpunctual, unready, untimely,
   viscid, viscose, viscous, wedged