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

horizontal transmission of the hepatitis B virus

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 top is designed with horizontal pleated detailing and cap sleeves, while the bottoms offer a simple, wide-leg silhouette with side pockets and a drawstring to adjust the fit to your liking. —Alicia Geigel, Southern Living, 17 Apr. 2026

Vertical Aerospace has scored a world-first as its full-scale tilt-rotor eVTOL completed a two-way piloted transition between vertical helicopter mode and horizontal airplane mode during a single continuous flight while under regulatory oversight. —David Szondy april 17, New Atlas, 17 Apr. 2026

The Fashion Nova baddie in horizontal sprawl off the Vertigo, for example, is an emblem for those in the know. —Julissa James, Los Angeles Times, 17 Apr. 2026

Several roundtable participants argued that deep vertical expertise — an intimate understanding of healthcare operations, for instance — is becoming more valuable than mastery of a horizontal, one-size-fits-all process. —Michael Jacobides, Fortune, 17 Apr. 2026

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