gyroscope

Coined in 1852 by physicist Léon Foucault from Ancient Greek γῦρος (gûros, "circle") and σκοπός (skopós, "watcher"), the word passed into French as gyroscope before being borrowed into English.

The name was built directly for the instrument Foucault invented, joining 'circle' and 'watcher' to describe a device that reveals rotation by watching how a spinning wheel holds its orientation.

The -scope half traces back to Greek skopós, "watcher," built from the verb root *speḱ- ("to watch"), the same deep root behind other -scope words that let us observe things otherwise hidden.