crosswise
flat
level
naiant
swimming
arrowlike
billiard table
bowling green
dead flat
dead level
dead straight
direct
earth
esplanade
even
flatland
flattened
floor
flush
ground
homaloid
homaloidal
horizontal axis
horizontal fault
horizontal line
horizontal parallax
horizontal plane
horizontal projection
in a line
ledge
level line
level plane
lineal
linear
mean sea level
parterre
plain
plane
platform
prairie
prone
rectilineal
rectilinear
right
rolled
ruler-straight
sea level
sea of grass
smooth
smoothed out
orientation
angular
central
circular
continuous
forward
internal
jagged
narrow
perpendicular
upper
vertical
consonantal
periodontal