<p><strong>Adjective</strong></p><ul><li>at right angles to the vertical; parallel to level ground.</li><li>flat or level: a horizontal position.</li><li>being in a prone or supine position; recumbent: His bad back has kept him horizontal for a week.</li><li>near, on, or parallel to the horizon.</li><li>of or relating to the horizon.</li><li>measured or contained in a plane parallel to the horizon: a horizontal distance.</li><li>(of material on a printed page, pieces on a game board, etc.) extending across, from the left to the right of the viewer.</li><li>of or relating to a position or individual of similar status: He received a horizontal promotion to a different department, retaining his old salary and title.</li><li>of or relating 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.</li></ul><p><strong>Noun</strong></p><ul><li>anything horizontal, as a plane, direction, or object.</li></ul>