horizontal

adjective

hor·​i·​zon·​tal ˌhȯr-ə-ˈzän-tᵊl 

ˌhär-

1

a

: of or relating to the apparent junction of earth and sky : situated near the horizon

b

: parallel to, in the plane of, or operating in a plane parallel to the horizon or to a baseline : level

horizontal distance

a horizontal engine

2

: relating to, directed toward, or consisting of individuals or entities of similar status or on the same level

horizontal mergers

horizontal hostility

3

medical : relating to or being transmission (as of a disease) by physical contact or proximity in contrast with inheritance

Genes are normally inherited from parents, but they can also be inserted into a genome by viruses, plasmids, and other foreign agents—a phenomenon called horizontal transfer.

—Stephan Reebs

compare vertical sense 4

horizontal noun

horizontality

ˌhȯr-ə-ˌzän-ˈta-lə-tē 

ˌhär-

noun

horizontally

ˌhȯr-ə-ˈzän-tᵊl-ē 

ˌhär-

adverb

Examples of horizontal in a Sentence

Recent Examples on the Web

The tartan motif featured severe horizontal and vertical lines, creating squares and including varying shades of muted red with hints of green. —Julia Teti, Footwear News, 9 Oct. 2025

Yeah, the time for prudent action, planning and working with comrades in different kinds of decision-making processes, developing new kinds of horizontal organizing. —Peter D'abrosca, FOXNews.com, 7 Oct. 2025

Grass plants grow new horizontal stems in autumn. —Megan Hughes, Better Homes & Gardens, 7 Oct. 2025

In a nearby alcove, a blue horizontal stripe was punctuated by key dates in red, such as 1906, when Finland became the first country in Europe in which women could run for political office. —Jennifer Wilson, New Yorker, 6 Oct. 2025

Word History

Etymology

see horizon

First Known Use

1555, in the meaning defined at sense 1a

Phrases Containing horizontal

• horizontal bar

Rhymes for horizontal

• consonantal
• periodontal
• quantal

Kids Definition

horizontal

1 of 2 adjective

hor·​i·​zon·​tal

ˌhȯr-ə-ˈzänt-ᵊl,

ˌhär-

1

: of or relating to the horizon

2

: parallel to the horizon : level

3

: being on the same level

horizontally

-ᵊl-ē

adverb

horizontal

2 of 2 noun

: a horizontal line or plane

Medical Definition

horizontal

adjective

hor·​i·​zon·​tal ˌhȯr-ə-ˈzänt-ᵊl, ˌhär- 

1

: relating to or being a transverse plane or section of the body

2

a

: relating to or being transmission (as of a disease) by physical contact or proximity in contrast with inheritance compare vertical

b

: of or relating to horizontal gene transfer

horizontally

-ᵊl-ē 

adverb

Legal Definition

horizontal

adjective

hor·​i·​zon·​tal ˌhȯr-ə-ˈzän-təl, ˌhär- 

: relating to, directed toward, or consisting of individuals or entities of similar status or on the same level

horizontally adverb