WordReference Random House Unabridged Dictionary of American English © 2020
- Astronomya level, as a surface of mercury, used in determining the altitudes of stars. Cf. level (def. 7).
- Astronomythe bubble in a sextant or octant for aerial use.
- AeronauticsAlso called flight indicator, gyro horizon. an instrument that indicates the banking and pitch of an aircraft with respect to the horizon.