horizontal

American  

[hawr-uh-zon-tl, hor-] / ˌhɔr əˈzɒn tl, ˌhɒr- /

adjective

1. at right angles to the vertical; parallel to level ground.

2. flat or level.

   a horizontal position.

3. being in a prone or supine position; recumbent.

   His bad back has kept him horizontal for a week.

4. near, on, or parallel to the horizon.

5. of or relating to the horizon.

6. measured or contained in a plane parallel to the horizon.

   a horizontal distance.

7. (of material on a printed page, pieces on a game board, etc.) extending across, from the left to the right of the viewer.

8. of or relating to a position or individual of similar status.

   He received a horizontal promotion to a different department, retaining his old salary and title.

9. Economics. of or relating to companies, affiliates, divisions, etc., that perform the same or similar functions or produce the same or similar products.

   Through horizontal mergers the company monopolized its field.

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noun

1. anything horizontal, as a plane, direction, or object.

horizontal British  

/ ˌhɒrɪˈzɒntəl /

adjective

1. parallel to the plane of the horizon; level; flat Compare vertical

2. of or relating to the horizon

3. measured or contained in a plane parallel to that of the horizon

4. applied uniformly or equally to all members of a group

5. economics relating to identical stages of commercial activity

   horizontal integration

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noun

1. a horizontal plane, position, line, etc

Other Word Forms

• horizontality noun
• horizontally adverb
• horizontalness noun
• subhorizontal adjective
• subhorizontally adverb
• subhorizontalness noun
• unhorizontal adjective
• unhorizontally adverb

Etymology

Origin of horizontal

1545–55; < Latin horizont- (stem of horizōn ) horizon + -al ¹

Explanation

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.

Example Sentences

This "selfless" sharing, known as horizontal gene transfer, can rapidly spread useful traits including genes that confer resistance to antibiotic drugs used to treat infections.

From Science Daily • Apr. 17, 2026

That’s because if high-income shoppers scale back their spending, then the other horizontal lines of the “E” — the lower and middle classes — may not have enough spending power to keep the economy afloat.

From MarketWatch • Apr. 3, 2026

Plenty of you who regularly plunk down thousands for a business-class seat care about just one thing, of course: horizontal sleep.

From The Wall Street Journal • Mar. 18, 2026

There was a horizontal stripe down the shirt, she said.

From BBC • Mar. 12, 2026

Two horizontal was some word meaning to remove afar off.

From "The Heart is a Lonely Hunter" by Carson McCullers