The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]