sprocket

Sprocket first appears in English in the 16th century, but its exact origin is unknown. It may be connected to Italian words for spool or spur, or to English words like spoke, spike, and spur.

The facts available don't reveal a documented shift in meaning over time, just a long-standing mystery about where the word came from.

It may share a root with English 'spoke' or 'spike', or with Italian words for spool ('rocchetto', 'spoletta') and spur ('sprone'), though none of this is certain.