The Collaborative International Dictionary of English v.0.48:

overwhelmed \overwhelmed\ adj.
   1. same as overpowered.

   Syn: overcome, overpowered, swamped, engulfed.
        [WordNet 1.5]

   2. defeated easily by a greatly superior opponent.

   Syn: routed.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Overwhelm \O`ver*whelm"\, v. t. [imp. & p. p. Overwhelmed; p.
   pr. & vb. n. Overwhelming.]
   [1913 Webster]
   1. To cover over completely, as by a great wave; to overflow
      and bury beneath; to ingulf; hence, figuratively, to
      immerse and bear down; to overpower; to crush; to bury; to
      oppress, etc., overpoweringly.
      [1913 Webster]

            The sea overwhelmed their enemies.    --Ps. lxxviii.
                                                  53.
      [1913 Webster]

            Fearfulness and trembling are come upon me, and
            horror hath overwhelmed me.           --Ps. lv. 5.
      [1913 Webster]

            Foul deeds will rise,
            Though all the earth o'erwhelm them.  --Shak.
      [1913 Webster]

            Gaza yet stands; but all her sons are fallen,
            All in a moment overwhelmed and fallen. --Milton.
      [1913 Webster]

   2. To project or impend over threateningly.
      [1913 Webster]

            His louering brows o'erwhelming his fair sight.
                                                  --Shak.
      [1913 Webster]

   3. To cause to surround, to cover. --Papin.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "overwhelmed":
   afloat, agape, aghast, agog, all agog, all up with, amazed,
   astonished, astounded, at flood, at gaze, awash, awed, awestruck,
   beat, beaten, beguiled, bested, bewildered, bewitched, breathless,
   broken-down, brokenhearted, captivated, confounded, crushed,
   cut up, defeated, deluged, desolated, discomfited, dismayed,
   done for, done in, down, drowned, dumbfounded, dumbstruck,
   enchanted, engulfed, enraptured, enravished, enthralled, entranced,
   fallen, fascinated, fixed, flabbergasted, flooded, floored, gaping,
   gauping, gazing, heart-stricken, heart-struck, heartbroken,
   hors de combat, hypnotized, in awe, in awe of, in spate, inflood,
   inundated, lambasted, lathered, licked, lost in wonder, marveling,
   mesmerized, on the skids, open-eyed, openmouthed, outdone,
   overborne, overcome, overexcited, overmastered, overmatched,
   overpowered, overridden, overthrown, overturned, overwrought,
   panicked, popeyed, put to rout, puzzled, rapt in wonder, routed,
   ruined, scattered, settled, shocked, silenced, skinned,
   skinned alive, spellbound, staggered, stampeded, staring, stricken,
   stupefied, surprised, swamped, swept, thunderstruck, trimmed,
   trounced, under a charm, undone, upset, washed, water-washed,
   whelmed, whipped, wide-eyed, wonder-struck, wondering, worsted