WHATCHAMACALLIT
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”
Source: WordNet® 3.1
Etymology
A shortened version of “what you may call it” or “what you might call it”. United States, 20th century (recorded in 1921).
Noun
whatchamacallit (plural whatchamacallits)
(slang) A metasyntactic term used for any object whose actual name the speaker does not know or cannot remember; a doodad, gizmo, thingamajig, thingy.
Synonyms
• See thingy
Source: Wiktionary