WordNet (r) 3.0 (2006):

gizmo
    n 1: something unspecified whose name is either forgotten or not
         known; "she eased the ball-shaped doodad back into its
         socket"; "there may be some great new gizmo around the
         corner that you will want to use" [syn: doodad,
         doohickey, doojigger, gimmick, gizmo, gismo,
         gubbins, thingamabob, thingumabob, thingmabob,
         thingamajig, thingumajig, thingmajig, thingummy,
         whatchamacallit, whatchamacallum, whatsis, widget]
    2: a device or control that is very useful for a particular job
       [syn: appliance, contraption, contrivance,
       convenience, gadget, gizmo, gismo, widget]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "gizmo":
   affair, apparatus, article, artifact, concern, contraption,
   contrivance, device, dingus, dofunny, dohickey, dojigger, dojiggy,
   domajig, domajigger, doodad, dowhacky, eppes, etwas, flumadiddle,
   gadget, gigamaree, gimcrack, gimmick, hand tool, hickey,
   hootenanny, hootmalalie, implement, instrument, jigger,
   material thing, means, mechanical device, object, power tool,
   precision tool, quelque chose, something, speed tool, thing,
   thingum, thingumabob, thingumadad, thingumadoodle, thingumajig,
   thingumajigger, thingumaree, thingummy, tool, utensil, whatchy,
   widget