Synonyms for Thingumajig (same or very similar meaning)
WordNet sense 1 (something unspecified whose name is either forgotten or not known):
doodad, doohickey, gimmick, gismo, gizmo, thingamabob, thingamajig, whatchamacallit, widget, gubbins, thingmabob, thingmajig, thingumabob, thingummy, whatsis, doojigger, whatchamacallumFrom the ODE community, based on WordNetadd/edit