- adjective lying flat or going from side to side, not up and down
- adjective parallel to the horizon, or at right angles to the vertical
- Pertaining to, related to, or situated at or near a horizon (1).
- Parallel to, or situated along the plane of a horizon (1) or a baseline. Also, operating in a plane parallel to a horizon or a base line.
- At a right angle to a vertical line.
- adjective lying flat or at a right angle to the vertical