What is "gyrostat"

Gyrostat \Gy"ro*stat\ (j[imac]"r[-o]*st[a^]t), n. [Gr. gy^ros ring, circle + "ista`nai 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.

1879, from gyro- + -stat.

n. A gyroscope fixed within a rigid case