An Etymological Dictionary of Astronomy and Astrophysics

1. Of or pertaining to the → horizon.
   

2. At right angles to the → vertical; parallel to level ground.
   

See also:
→ blue horizontal branch star, → extreme horizontal branch star, → field horizontal branch star, → horizontal branch, → horizontal branch star, → horizontal eclipse, → horizontal parallax, → horizontal refraction, → red horizontal branch star, → supra-horizontal branch star, → zero age horizontal branch star.

See also: From → horizon + → -al.