The Collaborative International Dictionary of English v.0.48:

Overreach \O`ver*reach"\ ([=o]`v[~e]r*r[=e]ch"), v. t. [imp. &
   p. p. Overreached, (Overraught, obs.); p. pr. & vb. n.
   Overreaching.]
   [1913 Webster]
   1. To reach above or beyond in any direction.
      [1913 Webster]

   2. To deceive, or get the better of, by artifice or cunning;
      to outwit; to cheat. --Shak.
      [1913 Webster]

   3. To defeat one's own purpose by trying to do too much or by
      trying too hard or with excessive eagerness; -- used
      reflexively; as, the candidate overreached himself by
      trying to plant false rumors, which backfired/
      [PJC]

WordNet (r) 3.0 (2006):

overreaching
    adj 1: revealing excessive self-confidence; reaching for the
           heights; "vaulting ambition" [syn: overreaching,
           vaulting]