Something whose name is unknown or forgotten.
(informal) Any device, contrivance, gadget, etc.
Something that one does not know the name of.
He used this, this... this thingamajig you saw him with the other day to fix the problem.
Origin of thingamajig
- Alteration of obsolete thingum (from thing) jig
From American Heritage Dictionary of the English Language, 5th Edition