The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Why gaddest thou about so much to change thy way?
                                                  --Jer. ii. 36.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. A pointed or wedge-shaped instrument of metal, as a steel
      wedge used in mining, etc.
      [1913 Webster]

            I will go get a leaf of brass,
            And with a gad of steel will write these words.
                                                  --Shak.
      [1913 Webster]

   3. A sharp-pointed rod; a goad.
      [1913 Webster]

   4. A spike on a gauntlet; a gadling. --Fairholt.
      [1913 Webster]

   5. A wedge-shaped billet of iron or steel. [Obs.]
      [1913 Webster]

            Flemish steel . . . some in bars and some in gads.
                                                  --Moxon.
      [1913 Webster]

   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.
      [1913 Webster]

   Upon the gad, upon the spur of the moment; hastily. [Obs.]
      "All this done upon the gad!" --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

GAD
    n 1: an anxiety disorder characterized by chronic free-floating
         anxiety and such symptoms as tension or sweating or
         trembling or lightheadedness or irritability etc that has
         lasted for more than six months [syn: generalized anxiety
         disorder, GAD, 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, gad]
    v 1: wander aimlessly in search of pleasure [syn: gallivant,
         gad, jazz around]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "gad":
   Ahasuerus, Ancient Mariner, Argonaut, Flying Dutchman, Goliard,
   Odysseus, Oisin, Ossian, Ulysses, bat, bat around, bird of passage,
   bum, count ties, divagate, drift, drifter, flit, floater,
   gad about, gadabout, gadfly, gallivant, go about, go the rounds,
   go-about, goad, hit the road, hit the trail, hobo, itinerant,
   jaunt, knock about, knock around, lash, maunder, meander, mooch,
   mover, nomadize, oxgoad, peregrinate, peregrinator, peregrine,
   pererrate, peripatetic, prick, prod, prowl, ramble, rambler, range,
   roam, roamer, rolling stone, rove, rover, rowel, run about,
   run around, runabout, saunter, spur, sting, straggle, straggler,
   stray, stroll, stroller, strolling player, traipse, tramp,
   troubadour, vagabond, vagabondize, visitant, walk the tracks,
   wander, wanderer, wandering minstrel, wandering scholar, wayfare,
   whip, whiplash



Easton's 1897 Bible Dictionary:

Gad
   fortune; luck. (1.) Jacob's seventh son, by Zilpah, Leah's
   handmaid, and the brother of Asher (Gen. 30:11-13; 46:16, 18).
   In the Authorized Version of 30:11 the words, "A troop cometh:
   and she called," etc., should rather be rendered, "In fortune
   [R.V., 'Fortunate']: and she called," etc., or "Fortune cometh,"
   etc.

     The tribe of Gad during the march through the wilderness had
   their place with Simeon and Reuben on the south side of the
   tabernacle (Num. 2:14). The tribes of Reuben and Gad continued
   all through their history to follow the pastoral pursuits of the
   patriarchs (Num. 32:1-5).

     The portion allotted to the tribe of Gad was on the east of
   Jordan, and comprehended the half of Gilead, a region of great
   beauty and fertility (Deut. 3:12), bounded on the east by the
   Arabian desert, on the west by the Jordan (Josh. 13:27), and on
   the north by the river Jabbok. It thus included the whole of the
   Jordan valley as far north as to the Sea of Galilee, where it
   narrowed almost to a point.

     This tribe was fierce and warlike; they were "strong men of
   might, men of war for the battle, that could handle shield and
   buckler, their faces the faces of lions, and like roes upon the
   mountains for swiftness" (1 Chr. 12:8; 5:19-22). Barzillai (2
   Sam. 17:27) and Elijah (1 Kings 17:1) were of this tribe. It was
   carried into captivity at the same time as the other tribes of
   the northern kingdom by Tiglath-pileser (1 Chr. 5:26), and in
   the time of Jeremiah (49:1) their cities were inhabited by the
   Ammonites.

     (2.) A prophet who joined David in the "hold," and at whose
   advice he quitted it for the forest of Hareth (1 Chr. 29:29; 2
   Chr. 29:25; 1 Sam. 22:5). Many years after we find mention made
   of him in connection with the punishment inflicted for numbering
   the people (2 Sam. 24:11-19; 1 Chr. 21:9-19). He wrote a book
   called the "Acts of David" (1 Chr. 29:29), and assisted in the
   arrangements for the musical services of the "house of God" (2
   Chr. 29:25). He bore the title of "the king's seer" (2 Sam.
   24:11, 13; 1 Chr. 21:9).


Hitchcock's Bible Names Dictionary (late 1800's):

Gad, a band; a troop