horizontal
hor.i.zon.tal \.ho.r-*-'za:nt-*l, .ha:r-\ \-*l-e-\ aj 1a: of, relating to,
or situated near the horizon 1b: parallel to, in the plane of, or
operating in a plane parallel to the horizon or to a base line : LEVEL {~
distance ~ engine} 2: relating to or consisting of individuals of similar
status in a hierarc hy {~ labor unions} - horizontal n
Webster's English Dictionary