The Collaborative International Dictionary of English v.0.48:

Congestion \Con*ges"tion\ (?; 106), n. [L. congestio: cf. F.
   congestion.]
   1. The act of gathering into a heap or mass; accumulation.
      [Obs.]
      [1913 Webster]

            The congestion of dead bodies one upon another.
                                                  --Evelyn.
      [1913 Webster]

   2. (Med.) Overfullness of the capillary and other blood
      vessels, etc., in any locality or organ (often producing
      other morbid symptoms); local hyper[ae]mia, active or
      passive; as, arterial congestion; venous congestion;
      congestion of the lungs.
      [1913 Webster]

WordNet (r) 3.0 (2006):

congestion
    n 1: excessive accumulation of blood or other fluid in a body
         part
    2: excessive crowding; "traffic congestion" [syn: congestion,
       over-crowding]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "congestion":
   amplitude, bar, barrier, blank wall, blind alley, blind gut, block,
   blockade, blockage, bottleneck, cecum, choking, choking off, clog,
   closeness, compactness, congestedness, consistence, consistency,
   constipation, costiveness, crowdedness, cul-de-sac, dead end,
   denseness, density, embolism, embolus, engorgement, firmness,
   flood tide, full, fullness, gluiness, glut, gorge, hardness,
   high tide, high water, hyperemia, impasse, impediment,
   impenetrability, impermeability, impletion, imporosity,
   incompressibility, infarct, infarction, jam, jammedness, obstacle,
   obstipation, obstruction, overbrimming, overburden, overcharge,
   overflow, overfreight, overfullness, overload, overspill,
   overweight, plenitude, plethora, relative density, repletion,
   satiety, saturation, saturation point, sealing off, solidity,
   solidness, specific gravity, spissitude, spring tide, stop,
   stoppage, strangulation, supersaturation, surcharge, surfeit,
   thickness, viscidity, viscosity, viscousness



The Free On-line Dictionary of Computing (30 December 2018):

congestion

    The condition that arises when the amount of
   data that senders want to send down a communication channel
   exceeds its capacity.  Typically this will result in some
   packets being delayed, thus increasing the average latency.

   (2014-05-04)