The Collaborative International Dictionary of English v.0.48:

Wapper \Wap"per\, v. t. & i. [freq. of wap, v.; cf. dial. G.
   wappern, wippern, to move up and down, to rock.]
   To cause to shake; to tremble; to move tremulously, as from
   weakness; to totter. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Wapper \Wap"per\, n. (Zool.)
   A gudgeon. [Prov. Eng.]
   [1913 Webster]