horizontal

/ˈhɔrəˌzɑntl/

/hɒrɪˈzɒntəl/

Other forms: horizontals

The opposite of vertical, something horizontal is arranged sideways, like a person lying down.

When you sleep (unless you're a horse), your body is horizontal: horizontal things are parallel to the ground or running in the same direction as the horizon. If you stack books horizontally, then they're on their side. You hear a lot about horizontal lines in geometry: If you picture a square, the top and bottom lines are horizontal lines.

Definitions of horizontal

1. adjective

   parallel to or in the plane of the horizon or a base line
   “a horizontal surface”

   synonyms:

   crosswise

   in the shape of (a horizontal piece on) a cross

   flat

   horizontally level

   level

   being on a precise horizontal plane

   naiant, swimming

   applied to a fish depicted horizontally

   antonyms:

   vertical

   at right angles to the plane of the horizon or a base line

   inclined

   at an angle to the horizontal or vertical position

   gradual

   (of a topographical gradient) not steep or abrupt

   steep

   having a sharp inclination

   plumb

   exactly vertical

   upended

   turned up on end

   unsloped, upright

   in a vertical position; not sloping

   atilt, canted, leaning, tilted, tipped

   departing or being caused to depart from the true vertical or horizontal

   aslant, aslope, diagonal, slanted, slanting, sloped, sloping

   having an oblique or slanted direction

   high-pitched

   set at a sharp or high angle or slant

   low-pitched

   set at a low angle or slant

   monoclinal

   of a geological structure in which all strata are inclined in the same direction

   pitched

   set at a slant

   salient

   represented as leaping (rampant but leaning forward)

   sidelong

   inclining or directed to one side

   skew, skewed

   having an oblique or slanting direction or position

   oblique

   slanting or inclined in direction or course or position--neither parallel nor perpendicular nor right-angled

   straight

   having no deviations
2. noun

   something that is oriented horizontally
   type of:

   orientation

   position or alignment relative to points of the compass or other specific directions