gyrostabilizer
noun
gy·ro·sta·bi·liz·er ˌjī-rō-ˈstā-bə-ˌlī-zər 
variants or gyrostat
ˈjī-rə-ˌstat
: a stabilizing device (as for a ship or airplane) that consists of a continuously driven gyro spinning about a vertical axis and pivoted so that its axis of spin may be tipped fore-and-aft in the vertical plane and that serves to oppose sideways motion
Word History
First Known Use
1921, in the meaning defined above