The Collaborative International Dictionary of English v.0.48:

Wag \Wag\, v. i.
   1. To move one way and the other; to be shaken to and fro; to
      vibrate.
      [1913 Webster]

            The resty sieve wagged ne'er the more. --Dryden.
      [1913 Webster]

   2. To be in action or motion; to move; to get along; to
      progress; to stir. [Colloq.]
      [1913 Webster]

            "Thus we may see," quoth he, "how the world wags."
                                                  --Shak.
      [1913 Webster]

   3. To go; to depart; to pack oft. [R.]
      [1913 Webster]

            I will provoke him to 't, or let him wag. --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Wag \Wag\, n. [From Wag, v.]
   [1913 Webster]
   1. The act of wagging; a shake; as, a wag of the head.
      [Colloq.]
      [1913 Webster]

   2. [Perhaps shortened from wag-halter a rogue.] A man full of
      sport and humor; a ludicrous fellow; a humorist; a wit; a
      joker.
      [1913 Webster]

            We wink at wags when they offend.     --Dryden.
      [1913 Webster]

            A counselor never pleaded without a piece of pack
            thread in his hand, which he used to twist about a
            finger all the while he was speaking; the wags used
            to call it the thread of his discourse. --Addison.
      [1913 Webster]

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.
   [1913 Webster]

         No discerner durst wag his tongue in censure. --Shak.
   [1913 Webster]

         Every one that passeth thereby shall be astonished, and
         wag his head.                            --Jer. xviii.
                                                  16.
   [1913 Webster]

   Note: Wag expresses specifically the motion of the head and
         body used in buffoonery, mirth, derision, sport, and
         mockery.
         [1913 Webster]

WordNet (r) 3.0 (2006):

wag
    n 1: a witty amusing person who makes jokes [syn: wag, wit,
         card]
    2: causing to move repeatedly from side to side [syn: wag,
       waggle, shake]
    v 1: move from side to side; "The happy dog wagged his tail"
         [syn: wag, waggle]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "wag":
   bad boy, banana, beat, bob, bobble, booger, brandish, buffoon,
   bugger, burlesquer, card, careen, caricaturist, clown, coggle,
   comedian, comic, cutup, dangle, devil, droll, elf, enfant terrible,
   epigrammatist, farceur, flap, flaunt, float, flourish, fluctuate,
   flutter, fly, funmaker, funnyman, gag writer, gagman, gagster,
   hood, hoodlum, hooligan, humorist, imp, ironist, jester, joker,
   jokesmith, jokester, kidder, knave, lampooner, lash, librate,
   little devil, little monkey, little rascal, lurch, madcap, minx,
   mischief, mischief-maker, nutate, oscillate, parodist, pendulate,
   pitch, pixie, practical joker, prankster, puck, punner, punster,
   quipster, rapscallion, rascal, reel, reparteeist, resonate, rock,
   rogue, roll, rowdy, ruffian, satirist, scamp, scapegrace, shake,
   show-off, squirm, swag, sway, swing, swinging, switch, take, toss,
   twist and turn, twitch, undulate, vacillate, vibrate, waggle,
   wagwit, wave, waver, wield, wiggle, wigwag, wisecracker, wit,
   witling, wobble, wriggle, writhe, zany



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

WAG
       Wild-Assed Guess (slang, Cygwin)