doodad, doohickey, doojigger, gimmick, gizmo, gismo, gubbins, thingamabob, thingumabob, thingmabob, thingamajig, thingumajig, thingmajig, thingummy, whatchamacallit, whatchamacallum, whatsis, widget(noun)

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"

thingamabob(Noun)

Placeholder word for a thing or person nonspecific, unknown or forgotten