Plain English Meaning

A spinning wheel held in a frame that only lets it tilt or pivot one way, instead of swinging freely in every direction. By limiting how it can move, the instrument can measure motion around just that one axis.

Full Definition

Gyroscopes mounted so they are free to rotate, or tilt, in only one plane rather than freely in any direction. The mounting deliberately limits the gyro's freedom of movement to a single axis, which causes the gyro to react to changes around that axis through precession. This type of mounting is used in turn indicators and turn coordinators, where the instrument must sense and display rotation about a specific aircraft axis.

Context Anchor

Seen when studying gyroscopic flight instruments, especially turn indicators and turn coordinators.

Derivation

means held or . -rigid means partly stiff -- not fully locked in place, but not fully free either. The phrase tells you the gyro is partly free to move, but only in a way.