1.adj. 1. Of, relating to, or near the horizon.
2.
a. Parallel to or in the plane of the horizon.
b. At right angles to a vertical line.
3. Occupying or restricted to the same level in a hierarchy: a horizontal study of verbal ability; a horizontal transfer by an employee.
4. Medicine Of or relating to transmission of infection by contact with or physical proximity to an infected individual or fomite.
n. Something, such as a line, plane, or object, that is horizontal.
[French, from Latin horizōn , horizont- , horizon; see horizon .]
hor′i·zon·tal′i·ty (-zən-tăl′ĭ-tē) , hor′i·zon′tal·ness n.
hor′i·zon′tal·ly adv.
