Wordnet 3.0
VERB (2)
1. 
 bid over an opponent's bid when one's partner has not bid or doubled; 
2. 
 bid higher than others; 
The Collaborative International Dictionary of English v.0.48:
Outbid \Out*bid"\, v. t. [imp. Outbid or Outbade (?); p. p.
   Outbid or Outbidden (?); p. pr. & vb. n. Outbidding.]
   To exceed or surpass in bidding; to bid a higher price.
   [1913 Webster]
         Prevent the greedy, and outbid the bold. --Pope.
   [1913 Webster]
WordNet (r) 3.0 (2006):
outbid
    v 1: bid over an opponent's bid when one's partner has not bid
         or doubled
    2: bid higher than others [ant: underbid]