Source : Webster's Revised Unabridged Dictionary (1913)

Gyrostat \Gy"ro*stat\, n. [Gr. ? ring, circle + ? to cause to
   stand.] (Physics)
   A modification of the gyroscope, consisting essentially of a
   fly wheel fixed inside a rigid case to which is attached a
   thin flange of metal for supporting the instrument. It is
   used in studying the dynamics of rotating bodies.