adj. & n.
--adj.
1. a parallel to the plane of the horizon, at right angles to the vertical (horizontal plane). b (of machinery etc.) having its parts working in a horizontal direction.
2 a combining firms engaged in the same stage of production (horizontal integration). b involving social groups of equal status etc.
3 of or at the horizon.
--n. a horizontal line, plane, etc.
Derivatives:
horizontality n. horizontally adv. horizontalness n.
Etymology: F horizontal or mod.L horizontalis (as HORIZON)