Gismo/Gizmo (Origins)

Gismo also gizmo, n. slang.

A mechnical device or part whose name is forgotten or unknown.  The origin of the word ‘gizmo‘ is unknown, according to the American Heritage Dictionary.

That would make the word, gizmo, itself, a lexical gizmo.  The word is, in other words, an example of what it means.  Signified and signifier, while separate, are joined by a thick band of connective flesh.  Like Siamese twins.