thwart
     n : a crosspiece spreading the gunnels of a boat; used as a seat
         in a rowboat [syn: {cross thwart}]
     v : hinder or prevent (the efforts, plans, or desires) of; "What
         ultimately frustrated every challenger was Ruth's amazing
         September surge"; "foil your opponent" [syn: {queer}, {spoil},
          {scotch}, {foil}, {cross}, {frustrate}, {baffle}, {bilk}]
Source: WordNet® 2.0