The Collaborative International Dictionary of English v.0.48:

Bet \Bet\, v. t. [imp. & p. p. Bet, Betted; p. pr. & vb. n.
   Betting.]
   To stake or pledge upon the event of a contingent issue; to
   wager.
   [1913 Webster]

         John a Gaunt loved him well, and betted much money on
         his head.                                --Shak.
   [1913 Webster]

         I'll bet you two to one I'll make him do it. --O. W.
                                                  Holmes.
   [1913 Webster]