3. Measured or contained in a plane of the horizon; as, horizontal distance. Horizontal drill, a drilling machine having a horizontal drill spindle. Horizontal engine, one the piston of which works horizontally. Horizontal fire, the fire of ordnance and small arms at point-blank range or at low angles of elevation.
(Science: physics) horizontal force, the distance in a horizontal plane to which a gun will throw a projectile. Horizontal water wheel, a water wheel in which the axis is vertical, the buckets or floats revolving in a horizontal plane, as in most turbines.