The Collaborative International Dictionary of English v.0.48:

Wag \Wag\, v. t. [imp. & p. p. Wagged; p. pr. & vb. n.
   Wagging.] [OE. waggen; probably of Scand. origin; cf. Sw.
   vagga to rock a cradle, vagga cradle, Icel. vagga, Dan.
   vugge; akin to AS. wagian to move, wag, wegan to bear, carry,
   G. & D. bewegen to move, and E. weigh. [root]136. See
   Weigh.]
   To move one way and the other with quick turns; to shake to
   and fro; to move vibratingly; to cause to vibrate, as a part
   of the body; as, to wag the head.
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         No discerner durst wag his tongue in censure. --Shak.
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         Every one that passeth thereby shall be astonished, and
         wag his head.                            --Jer. xviii.
                                                  16.
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   Note: Wag expresses specifically the motion of the head and
         body used in buffoonery, mirth, derision, sport, and
         mockery.
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