The Collaborative International Dictionary of English v.0.48:

Evener \E"ven*er\, n.
   1. One who, or that which makes even.
      [1913 Webster]

   2. In vehicles, a swinging crossbar, to the ends of which
      other crossbars, or whiffletrees, are hung, to equalize
      the draught when two or three horses are used abreast.
      [1913 Webster]