gyroscope

Concise Oxford English Dictionary © 2008 Oxford University Press:
gyroscope/ˈʤʌɪrəskəʊp/

▶noun a device, used to provide stability or maintain a fixed orientation, consisting of a wheel or disc spinning rapidly about an axis which is itself free to alter in direction.

– derivatives
gyroscopic adjective,
gyroscopically adverb.

– origin C19: from Fr., from Gk guros ‘a ring’ + mod. L. scopium (see -scope).