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:

Overpower \O"ver*pow`er\, n.
   A dominating power. --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overpower
    v 1: overcome by superior force [syn: overpower, overmaster,
         overwhelm]
    2: overcome, as with emotions or perceptual stimuli [syn:
       overwhelm, overpower, sweep over, whelm, overcome,
       overtake]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "overpower":
   amaze, be strong, bear down, beat, best, conquer, crush, daze,
   deck, defeat, drown out, dumbfound, floor, jam, master, nonplus,
   outroar, outshout, overcome, overmaster, overmatch, overset,
   overthrow, overturn, overwhelm, pack a punch, prevail, put down,
   quell, send flying, shout down, silence, stagger, strike, stun,
   stupefy, subdue, subjugate, surmount, trip, trip up, upset,
   vanquish, whelm, worst