A small gadget or object whose name you can't remember or don't know; a thingamajig.
First appeared in American slang around 1920s, likely derived from earlier nonsense words like 'doodad.' The origin is uncertain but probably related to reduplicative sound patterns used for objects of unknown purpose.
English has dozens of these silly placeholder words—doohickey, thingamabob, whatchamacallit—and they're all markers of when our brains fail to retrieve the actual name; linguists call this phenomenon the 'tip of the tongue' effect, and these words are like verbal shrugs.
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