at right angles to the vertical; parallel to level ground.

flat or level

a horizontal position.

being in a prone or supine position; recumbent

His bad back has kept him horizontal for a week.

near, on, or parallel to the horizon.

of or pertaining to the horizon.

measured or contained in a plane parallel to the horizon

a horizontal distance.

(of material on a printed page, pieces on a game board, etc.) extending across, from the left to the right of the viewer.

of or pertaining to a position or individual of similar status

He received a horizontal promotion to a different department, retaining his old salary and title.

Economics . of or pertaining to companies, affiliates, divisions, etc., that perform the same or similar functions or produce the same or similar products

Through horizontal mergers the company monopolized its field.

anything horizontal, as a plane, direction, or object.

adjective

upright , vertical

adjective

accumbent , aligned , even , flush , level , parallel , plane , recumbent , regular , smooth , straight , uniform , decumbent , procumbent , prone , prostrate , endwise , flat , supine