Source : Webster's Revised Unabridged Dictionary (1913)

Gad \Gad\, v. i. [imp. & p. p. {Gadded}; p. pr. & vb. n.
   {Gadding}.] [Prob. fr. gad, n., and orig. meaning to drive
   about.]
   To walk about; to rove or go about, without purpose; hence,
   to run wild; to be uncontrolled. ``The gadding vine.''
   --Milton.

         Why gaddest thou about so much to change thy way?
                                                  --Jer. ii. 36.

Gad \Gad\, n. [OE. gad, Icel. gaddr goad, sting; akin to Sw.
   gadd sting, Goth. gazds, G. gerte switch. See {Yard} a
   measure.]
   1. The point of a spear, or an arrowhead.

   2. A pointed or wedge-shaped instrument of metal, as a steel
      wedge used in mining, etc.

            I will go get a leaf of brass, And with a gad of
            steel will write these words.         --Shak.

   3. A sharp-pointed rod; a goad.

   4. A spike on a gauntlet; a gadling. --Fairholt.

   5. A wedge-shaped billet of iron or steel. [Obs.]

            Flemish steel . . . some in bars and some in gads.
                                                  --Moxon.

   6. A rod or stick, as a fishing rod, a measuring rod, or a
      rod used to drive cattle with. [Prov. Eng. Local, U.S.]
      --Halliwell. Bartlett.

   {Upon the gad}, upon the spur of the moment; hastily. [Obs.]
      ``All this done upon the gad!'' --Shak.

Source : WordNet®

GAD
     n 1: an anxiety disorder characterized by chronic free-floating
          anxiety and such symptoms as tension or sweating or
          trembling of light-headedness or irritability etc that
          has lasted for more than six months [syn: {generalized
          anxiety disorder}, {anxiety reaction}]
     2: a sharp prod fixed to a rider's heel and used to urge a
        horse onward; "cowboys know not to squat with their spurs
        on" [syn: {spur}]