The Collaborative International Dictionary of English v.0.48:

Overpower \O`ver*pow"er\, v. t. [imp. & p. p. Overpowered; p.
   pr. & vb. n. Overpowering.]
   To excel or exceed in power; to cause to yield by superior
   power; to vanquish; to subdue; as, the light overpowers the
   eyes. "And overpower'd that gallant few." --Wordsworth.
   [1913 Webster]

   Syn: To overbear; overcome; vanquish; defeat; crush;
        overwhelm; overthrow; rout; conquer; subdue.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

overpowered \overpowered\ adj.
   1. rendered powerless especially by an excessive amount or
      profusion of something.

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

   2. Having more than the required power; as, an overpowered
      hot rod. [Colloq.]
      [PJC]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "overpowered":
   all up with, beat, beaten, bested, confounded, defeated,
   discomfited, done for, done in, down, fallen, fixed, floored,
   hors de combat, lambasted, lathered, licked, on the skids, outdone,
   overborne, overcome, overexcited, overmastered, overmatched,
   overridden, overthrown, overturned, overwhelmed, overwrought,
   panicked, put to rout, routed, ruined, scattered, settled,
   silenced, skinned, skinned alive, stampeded, trimmed, trounced,
   undone, upset, whelmed, whipped, worsted